Rules on Civil Procedure
Section 12. Proof of filing. - The filing of a pleading or paper shall be proved by its existence in the record of the case. If it is not in the record, but is claimed to have been filed personally, the filing shall be proved by the written or stamped acknowledgment of its filing by the clerk of court on a copy of the same; if filed by registered mail, by the registry receipt and by the affidavit of the person who did the mailing, containing a full statement of the date and place of depositing the mail in the post office in a sealed envelope addressed to the court, with postage fully prepaid, and with instructions to the postmaster to return the mail to the sender after ten (10) days if not delivered. (n)