What can I do if the employer is creating the problem while relieving me?

I have worked for a company sincerely and worked hard, where there is condition for 2 years bond period. Completed the bond period and worked 2 months more after the bond period. I kept the resignation and they have accepted orally. I also served for the Notice period of 2 months according to their employment contract. They stretched up to last working day and on the last working day they said that your resignation is not accepted. Due to this I lost the opportunity in the new company and due to this pandemic outbreak (Corona) I am not getting opportunity. Can I go legally for this? If Yes, how can I approach?

What exactly is the legal remedy the poster wants?
Had he mentioned in his resignation that his notice period started from the date of submission of the resignation letter and ends on the effective date of resignation?
If so the employer cannot simply reject his resignation at the end of the notice period.
If the poster is bold enough, he can simply walk out and join elsewhere.
He can also sue the employer for rejecting his resignation without any valid reason which resulted in his losing a better job.

Not providing Relieving Letters even after I worked as per their company norms and resigned as per the process. Before the lockdown I kept the Resignation and they have accepted orally. On the last working day of my Notice period saying that your resignation is not accepted. Said that until the project get released we don't relieve you. And started allegations over me. I asked for the Project release date, but they said due this pandemic outbreak it is ameturish to decide on the date. Infact they don't want to relieve me. So I left the company on my last working day and I didn't turn on to the work from that day. It's one month but they are not providing the Relieving Documents and started more allegations over me. How can I approch to get my relieving documents.