Rejected my request for relieving letter

Sir, I use to work in private bank. I started getting lower back pain in start of 2018. So bad that I was not able to sleep/seat or travel in Mumbai crowded tran. I told them that due to nature of work I am in ie., Calling I can't seat for long hours and request for internal transfer. Which eventually does not happen and as I continue with job by taking medication and physiotherapist treatment. In October 2019 it was like final nail in my coffin and I was not able to report to work. Few emails to and fro with my TL, he wants me to confirm final date of joining which I told him I cannot as the situation is bad and he advise me one date on email if I don't report or confirm any thing he will mark me absconding and no relieving letter will be issued. I have submitted my CT scan report, surgeon and physiotherapist follow up report also to them. But he came after few days saying he want letter from from spine surgeon that I won't be able to continue job literally he was asking me to submit letter that I am incapable of doing job in future. Then in January 2020 my records was updated as absconding and yesterday HR representative after so many follow up has refused to give me relieving letter. I work with them for 3.5yrs and now it's more than year I'm unemployed. Please suggest what to do??