Defendant contends the trial court erred in refusing to dismiss plaintiffs action for increased child support and for attorney fees, and in issuing the further orders for garnishment, and for his arrest for the reason that defendant has not been properly served. Defendant’s contention raises the issue of whether the trial court properly exercised jurisdiction over the person of the defendant. We find the defendant’s contention to be without merit. The trial court properly exercised personal jurisdiction.
The defendant is a chief petty officer in the U.S. Navy, stationed aboard the U.S.S. Skate (SSN-578) in Pearl Harbor. Defendant claims Wyoming as his official residence. The notice of hearing was mailed to the U.S.S. Sea Dragon (SSN-584).
Defendant contends this proceeding is a new civil action and that G.S. 1A-1, Rule 4(j) requires that initial pleadings, when mailed to an out-of-state defendant, be mailed by “registered or certified mail, return receipt requested, addressed to the party to be served, and delivering to the addressee only.”
*406“[W]here a statute provides for service of summons ... by designated methods, the specified requirements must be complied with or there is not a valid service.” (Citation omitted.)
In the confession of judgment, defendant states that he was formerly a resident of Wake County, North Carolina, and is now on active duty with the U.S. Navy. The judgment further states that the amount of support paid by defendant “shall be subject to change from time to time, based upon the income of the defendant and the needs of the children.” The judgment was a court decree of the Wake County District Court.
The documents filed in this cause do not initiate a new cause of action and need not meet the same requirements as service of process in a new cause. It is well settled that a judgment concerning the custody or support of a minor child is not final but may be altered by the showing of a substantial change of circumstances. Stanback v. Stanback, 287 N.C. 448, 456, 215 S.E. 2d 30 (1975). Jurisdiction over the person of the defendant began and remained with the North Carolina court when the defendant knowingly and voluntarily signed a confession of judgment pursuant to G.S. 1A-1, Rule 68.1. Pulley v. Pulley, 255 N.C. 423, 429, 121 S.E. 2d 876 (1961).
G.S. 1A-1, Rule 5(b) provides, among other things, that:
With respect to all pleadings subsequent to the original complaint and other papers required or permitted to be served ... service upon ... a party may also be made by delivering a copy to him or by mailing it to him at his last known address ....
Regarding service by mail, Rule 5(b) states that it is complete “upon deposit of the pleading or paper enclosed in a postpaid, properly addressed wrapper in a post office or official depository under the exclusive care and custody of the United States Postal Service.” The certificate of service and affidavit provided by plaintiffs attorney plainly indicate that a copy of the motion in the cause, notice of the initial hearing, the order *407to appear and produce documents, and the 6 November order denying defendant’s motion for a stay were mailed to the defendant at his last known address, the U.S.S. Sea Dragon. The defendant does not deny receipt of the papers and, in fact, acknowledges receipt. Defendant was properly served.
 Defendant argues next that the confession of j udgment and the subsequent entry of judgment are defective and not binding on him. However, defendant acknowledged in the instrument that he had read it and the matters contained therein were true to the best of his knowledge. For years defendant paid the monthly installments for child support without challenge to the judgment.
In Whitehead v. Whitehead, 13 N.C. App. 393, 399, 185 S.E. 2d 706 (1972), this Court held that a husband who has ratified, accepted or acquiesced in a child support decree by confession is estopped to challenge the validity of the judgment on the ground of informalities or irregularities in either the confession of judgment or the decree itself. To be effective the challenge to the confession of judgment must show fraud, mistake or oppression. See also Pulley, supra. Defendant has not pleaded any of these defenses. The defendant was properly before the court and under its jurisdiction.
Defendant argues further that the presiding judge of the Wake County District Court erred when he found that defendant’s letter of 26 October 1979 seeking relief under the Soldiers and Sailors Civil Relief Act of 1940, 50 U.S.C. App., Section 521 [hereinafter Act], constituted a voluntary appearance and denied his motion for a stay. We do not address the issue of whether the letter constituted a general appearance. As we stated earlier, the district court gained personal jurisdiction of defendant when the confession of judgment was signed.
 We do not find error in the presiding judge’s action denying defendant’s application pursuant to the Act. “The Act cannot be construed to require continuance on mere showing that the defendant [is] ... in the military service.” Boone v. Lightner, 319 U.S. 561, 87 L. Ed. 1587, 63 S. Ct. 1223, reh. denied 320 U.S. 809 (1943). “While the Act mandates a continuance ... where military service would cause a party to be absent, it also empowers the trial judge to deny the continuance if, in his opinion, ‘the *408ability of the ... defendant to conduct his defense is not materially affected by reason of his military service.’ ” Booker v. Everhart, 33 N.C. App. 1, 8, 234 S.E. 2d 46 (1977), rev’d, on other grounds 294 N.C. 146, 240 S.E. 2d 360 (1978).
The presiding judge found that defendant is voluntarily enlisted and has no plans to retire for the next seven years. The judge further found that defendant is entitled to thirty days’ leave each year and has military transportation available to him at reduced or no cost. Based on the facts, the judge did not abuse his discretion in denying the stay. In fact, it appears to this Court that the judge was generous in delaying the hearing until 21 November 1979, and that defendant’s use of the Act was dictated by strategy rather than the necessities of military service. Such use was improper. See Booker, at p. 9.
For the reasons set out above, the orders of the presiding judge addressed herein are affirmed.
The orders of the trial court are
Judges ARNOLD and Martin (Harry C.) concur.