Notice Period - Buy Out

Hi, I am Devang. I resigned from my company on 22nd Oct'2022 and I clearly mentioned in the mail that I want to leave by 25th Nov'2022. When my HR sent me the the amount breakup that I need to pay for the remaining days in my 3 months notice period, they have added things like HRA, Bonus, PF, allowances (education and special), LTA, gift voucher, other reimbursements and basic pay. Nothing about this was mentioned in my contract letter. My contract letter says "You will be required to give a written notice of not less than 90 days. Salary in lieu of notice period if proposed to be paid by you, shall be at the sole discretion of the company. The decision of the company shall be final and binding to you." The settlement amount breakup for my notice period buyout that they have shared is calculated on my total CTC and not basic pay. I heard that companies can calculate the same on gross pay also but that was not mentioned clearly in my contract. Please help me as my company is threatening me to file legal charges against me and ruin my career. What can they legally ask me? What powers do I have? Pls help!