Forceful extension of Notice Period, Patent Theft

In terms of the Indian Patents Act, employee can be the owner of the patent if he is the true and first inventor.  However, it depends whether the employee did the research and come up with the invention as a part of employment using employers resources and facilities. This therefore will be a question of facts and there cannot be a straight jacket answer applying to all facts here.  If indeed you are the patent owner in light of the facts applying to your case, there will be ways to reinstate you as rightful owner and/ or claim hefty damages. 

About not relieving you and acting against the terms of employment contract, the same constitutes breach of contract entitling you to damages.  However, it needs to be checked thoroughly if your employer could ask you to serve a longer notice period under a given situation.  There may be clauses in the contract providing for special situations in which such extended notice period could apply.  If there are no clauses, you could surely sue the company for damages for this limited point or take it to arbitration(in case of there being an arbitration clause in the contract) but unfortunately, you will end up spending much greater time in litigation and gain little here.