and “Third Notice”[33] tending to indicate that the registered mail was returned to sender because it was unclaimed despite the notices sent by the postmaster to the addressee.  Petitioner should not have relied on these notations to support the presumption of constructive service.[34]  The envelope does not constitute sufficient proof that a first notice was sent by the postmaster, much less, that there was completeness of service.[35]             A party who relies on constructive service or who contends that his adversary has received a copy of a final order or judgment upon the expiration of five days from the date the addressee received the first notice sent by the postmaster must prove that the first notice was actually received by the addressee. [36]     For completeness of constructive service, there must be conclusive proof that Anita’s former counsel had actually received the notice.[37] Such proof requires a certified or sworn copy of the notice given by the postmaster to the addressee.  Thus, Section 13 of Rule 13 provides:               Proof of service. –  x x x  If service is made by registered mail, proof shall be made by such affidavit and the registry receipt issued by the mailing office.  The registry return card shall be filed immediately upon its receipt by the sender, or in lieu thereof of the unclaimed letter together with the certified or sworn copy of the notice given by the postmaster to the addressee.  (Emphasis supplied)     There must be compliance with Section 13 of Rule 13 on proof of service by registered mail.  As the Court ruled in Dela Cruz v. Dela Cruz:[38]   In the present case there is no proof of the actual receipt of the notice of the registered mail by counsel for the defendants, Atty. Belen. The trial court merely relied on the notations on the wrapper or envelope of the returned order of September 21, 1965 consisting of “R & S”, “unclaimed” and the stamped box with the wordings “2nd notice” and “last notice” tending to indicate that the registered mail was returned to sender because it was unclaimed inspite of the notices sent by the postmaster to the addressee therein. The trial court, on the basis of said notations, assumed that the first notice of the postmaster must have been received by