Company is not releasing me in 30 days forcing me to work for 90 days notice period

Hi, I am working in a MNC where the notice period is of 90 days. I have to join my new company within 30 days. Hence, I am willing to serve 30 days and will buyout the rest of the notice period. However, my company is forcing me to work for 90 days & forcing me to complete the project end to end before leaving. My manager have threatened me that she will give me relieving letter even after buying out the notice period. In my contract, it is mentioned as '5.7 Without prejudice to the provisions of Section 4.1, 4.2 and 5.2, if the Executive terminates his/her employment pursuant to Section 4.1 (without cause), then IQVIA may at its sole option, either require the Executive to: (a) serve the notice period specified in Section 4.1 (whether such notice period is within the Probation Period or at any time thereafter) in whole or part; or (b) may pay the Executive an amount equivalent to the gross salary that would have been owed to the employee for the duration of the aggregate notice period specified in Section 4.1 in lieu of the Executive serving the said notice period. 5.8 It is expressly acknowledged and agreed that the rights of IQVIA set out in Section 5.7 (a) and (b) may be exercised in whole or in part by IQVIA and where IQVIA requires the Executive to only serve a part of his/her notice period pursuant to Section 5.7 (a), then for the remainder of the notice period IQVIA shall pay amounts in lieu of notice on a pro-rated basis' Please let me know the basic right of employee upon resigning and after buyout also if I don't get releasing letter is it legally right?