Official Receipt is the best evidence to prove Payment.

 "We have reviewed the records of the case and we are more convinced with the factual findings of the Court of Appeals. Rosita P. Lee (Lee), respondent’s Treasurer, explained that it is the company practice to prepare four copies of SALES INVOICES. Respondent’s delivery personnel would bring two copies of the Sales Invoices at the time of the delivery – the original and a duplicate copy. Both copies were supposed to be signed by petitioner’s representative. Respondent’s delivery personnel would leave the duplicate copy with petitioner and retain the original copy of the Sales Invoice. Whenever respondent made a collection, it would prepare a STATEMENT  OF ACCOUNT and it would send the Statement of Account, together with the original copies of the SALES INVOICES, to petitioner.8

Considering this practice, it is impossible for respondent to present the original or duplicate copies of the Sales Invoices which bore the signatures of petitioner’s representative because they are both in petitioner’s possession. The Sales Invoices accepted by the trial court, which bore the signatures of petitioner’s representatives, were retained by respondent and not delivered to petitioner because they were not yet due at the time the Statement of Account was prepared.

The Court also notes that the SALES INVOICES state: "PAYMENT NOT VALID WITHOUT OUR OFFICIAL RECEIPT."9 The SALES INVOICES are NOT EVIDENCE OF PAYMENT . They are only evidence of the RECEIPT OF THE GOODS. The BEST EVIDENCE TO PROVE PAYMENT of the goods is the OFFICIAL RECEIPT. Petitioner failed to present any official receipt to prove that it had already paid the goods to respondent.

We agree with the Court of Appeals’ observation that petitioner DID NOT OBJECT to the entries in the STATEMENTS OF ACCOUNT. Petitioner did not do anything despite the clear reminder in the Statements of Account which states: "IMPORTANT: If this statement does not agree with your record, please notify us at once."10 Petitioner remained SILENT for FOUR YEARS from the time it received the Statements of Account until the filing of the case against it. Petitioner did not even bother to respond to the DEMAND LETTER sent by respondent. Petitioner’s SILENCE is uncharacteristic of persons who have just been asked to pay an obligation to which they are not liable.11 In one case,12 the petitioner RECEIVED a STATEMENT OF ACCOUNT from the respondent WITHOUT PROTEST, and the petitioner DID NOT CONTROVERT the respondent’s demand letter. The Court applied ESTOPPEL IN PAIS where one, by his acts, representations or admissions, or by his own SILENCE when he ought to speak out, intentionally or through culpable negligence, induces another to believe certain facts to exist and such other rightfully relies and acts on such belief, so that he will be prejudiced if the former is permitted to deny the existence of such facts.13 We agree with the Court of Appeals that petitioner’s SILENCE for FOUR YEARS is TANTAMOUNT TO ADMISSION of the entries in the Statements of Account sent by respondent."

EL ORO ENGRAVER CORPORATION, petitioner, vs. COURT OF APPEALS and EVERETT CONSTRUCTION SUPPLY, INC., respondents. G.R. No. 125267, February 18, 2008. 

https://lawphil.net/judjuris/juri2008/feb2008/gr_125267_2008.html