that their dismissal was unlawful for failure of private respondents to comply with the twin requirements of due process, i.e., notice and hearing. Petitioners allege that they were not given any opportunity to be heard by private respondents prior to their termination. Spped jo Petitioners further contend that public respondent gravely abused its discretion in not giving evidentiary weight to the affirmation of eleven (11) former employees, as well as three (3) other witnesses as to the existence of the optional early retirement policy. Said witnesses were allegedly present when Captain Estaniel announced the optional early retirement policy under the CEIP. On the other hand, while the 11 former employees were not actually present at the announcement thereof, they attested to the fact that they were informed of said policy by the officers of private respondents. Petitioners point out that these former employees did not stand to benefit from the policy; thus, in the absence of any vested interest on their part, their affidavits should have been given more weight than the self-serving denials of private respondents officers. Petitioners also invoke the principle of estoppel. According to petitioners, estoppel bars a party who has, by his own declaration, act or omission, led another to believe a particular thing to be true, and to act upon such belief, from denying his own acts and representations to the prejudice of the other party who relied upon them. In the instant case, petitioners allege that since they relied in good faith and acted on the basis of the representations of private respondents that an optional early retirement plan indeed existed, the principle of estoppel in pais is clearly applicable to them. Petitioners, likewise, maintain that public respondent NLRC seriously erred in invoking the parol evidence rule against them as there is no written agreement to speak of on optional retirement so as to make this rule applicable. Petitioners declare that "nowhere in the contract (of enlistment) is there any mention of the specific terms of the CEIP, particularly the provisions on the extent of benefits to be received by the seamen" but rather, the "specific details are contained in a separate document which is in the nature of an inter-office memorandum that is unilaterally issued by private respondents." Petitioners further claim that public respondent NLRC abused its discretion in failing to consider that even in the absence of the optional early retirement policy, petitioners are still entitled to receive 100% of their total credited contributions to the CEIP either under Sec. III, par. (c) of the CEIP, or par. 2 (h) of the Letter-Memorandum dated March 9, 1977. Said memorandum which was signed by the then President/Chairman of TransGlobal, Inocencio P. Estaniel (now deceased), itemized the benefits that may be availed of by eligible employees. Paragraph 2 (h) thereof allegedly guarantees that an employee who is terminated for any reason, other than misconduct on his part, will be given 100% of the Total Credited CEIP Contributions for sixty (60) months of credited service. On the other hand, Section III, paragraph (c) of the Consecutive Enlistment Incentive Plan provides: