F&F settlement and relieving letter

Hello Team, I separated from my company as of July 15th, 2020. I received the F&F settlement mail in about 40 days from then- however I am still contesting the amount because of a contract I had undertaken. The contract specifically states that 'we require you to undertake this agreement to repay cost (on a pro-rated basis) to the company should you decide to resign and leave the company within 24 months from the completion of date'. (I had only completed 12 months till before separating) It does not mention that I am liable to repay any cost should the company decide to ask me to resign/ relieve me (for whatever reasons). The company has accepted on mail that they asked me to resign but still holds me liable to pay the amount on pro-rata basis. (I was adamant on receiving an extension of 30 days to travel back to Mumbai in the middle of Covid, also willing to accept loss of pay while already having 26 days of leaves to be availed. But it was not acceptable to the company.) My question is, that can they withhold my relieving letter till after the dues are cleared, or are they obliged to give it to me either way. Because I don't want to have to pay just to get the letter, unless that's my only option.