Short notice period for key employee

Dear sir, My total experience is 15 years and i have been employed in this company for 7 years my date of joining was 26.07.2016. Initially as per appointment letter my notice period was 1 month later in 2022 march a revised notice period of 3 months along with termination clause was added. The acknowledgement was taken from all employees on their portal. Now my question are a follows, 1. I have resigned on 3 rd may by giving 59 days notice period which is completing on June 30. They have not given any acceptance and neither have communicated anything in writing. Verbally they are saying you cannot leave until notice period of 90 days is completed. 2. Despite 2 reminders they have not appointed any one to take my hand over, as I am the only key person left as my team of 2 employees resigned 2 years before despite my verbal request to provide replacement no one was appointed which made me they key employee, now only i look after company bills to client, and the project is on the verge of completion and many closing task are Pending, also before my resignation they were saying this entire team will be transferred to another site location as this project is in loss. they are saying it may turn bad for my future if i go without serving full notice. Can they push any legal notice or unwanted charges on me? 3. I am confused as my new employer is not willing to wait more than the joining date I have given. They are ready to take me on board without relieving letter or experience letter. Please suggest me advice how to deal and what to decide as they are threatening me