I was working as a part-time trainer but never received an offer letter despite asking multiple times. I have now resigned; however, I never received a letter of appointment. I still gave them a 15-day notice period, but before completing the full 15 days, they issued me a relieving letter on the 11th day. They mentioned in the relieving letter that I will receive my full and final settlement after 45 days, which I consider unjust. I have not accepted their relieving letter and have asked them to clear my dues within a week. However, they are denying my request, stating that the institute is not even government-approved. Please suggest how I can claim my salary from them.