Denying of payment of notice pay

I resigned from my organisation and was ready to serve my notice period that is for 3 month, suddenly my company decided to relieve me immediately, i also gave them offer of assigning me to different project while in notice period at that time they denied and asked me to submit my laptop and leave. On being relieved early i asked for 3 month of notice pay. They are denying saying they are not bound to pay anything as i have resigned and they can release me anytime. Now after a week they are asking me to work remotely then only they will pay me. But in my current situation i have committed to other company that i can join them immediately and waiting for offer letter from other company. These people are mentally torturing me as well as making it difficult for me financially. In my offer letter i have a section saying Notice Period / Termination which says ​ — This contract of employment between you and the Company may be terminated by either party by giving 90 days’ notice or gross monthly salary in lieu thereof. Now they are also not giving me my relieving letter, as they are saying we will give you once you accept the full and final settlement. I don't know what to do.