Thank you for your suggestions,
Admissionado,
MBAGuide and
MBAandBeyond. And my apologies for the delay in getting back. The rush to meet the application deadlines of IIMs A, B and C. I called up the PGPx admission offices of all three: IIM B said I have payslips, so nothing to worry. IIM A and C listened to me patiently and asked me to send them a detailed mail with a list of documents that are available. IIM C said on the phone whether my case will be considered depends on the panel, nonetheless they asked me to recap my case on the mail for their record. IIM A folks were also understanding and have sought time to get back to me. The lady on the ISB admission phone number was very unkind and combative. I asked her if the suggestions made by you all (such as reference from other ex-employees, the founder's email identifying me as a head of department will do) will do, and she went into full condescending mode, saying these hacks don't work anywhere, no relieving letter means no admission.
Of the four colleges I wanted to try (IIM A, B, C and ISB), only IIMB said payslip will do. ISB has said a clear no and IIM A and C have said "let's see". Full-on panic. I spoke with a lawyer, he said that if my company's owner is in such a vindictive mood, a legal notice won't help me either since such a notice does not compel the receiver to do anything.
I want to thank you all for your suggestions. I wish I had the funds to avail of your services. After more than five years of working for peanuts (the founder dangled a carrot in front of me) and then two years of freelancing, I'm not in a position to spend. Thank you again for your tips. Hoping I sail past this situation!