Can I Challenge 3 Months Notice Period With Buyout

My current company has a policy of 3 months notice period. I have already resigned but my future company wants me to join within 50 days and are ready to buy out. But my current company is not releasing me and forcing me to serve 90 days notice period. On my Offer Letter, its mentioned : "On confirmation, your services will be liable for termination on a three months’ notice from either side or remuneration in lieu thereof, payable as per the company’s rules. However, when situations warrant, as in the case of breach of policies, the company may decide to terminate the engagement with immediate effect" Please suggest Can I serve 50 days and pay them for the rest 40 days NP. Can they still hold my Exp and Relieving Letter?