Company denying relieving letter

Hi, I need help. I joined this BPO in August 2021 and at that time there were no jobs in the market due to Covid. This company offered me less than my last drawn saying that this is the last we can give. I accepted as I was in need. I referred my friend who got a call within the same month and she was offered way better than I was irrespective of the last cut off they told me. I raised this with my Manager, he raised it with his Manager and I got an answer saying this cannot be rectified now as you accepted the offer and we cannot raise salary correction as you're not tenured enough. I got denied for my concern here which impacted me financially. Now, I got a job offer from a reputed company and they're offering me a good hike on my last drawn and my joining is next month. Problem is, I have 2 months notice period here, and there is no buy out option. They're threatening me saying they will not issue me the relieving letter if I do not complete my notice period, but I cannot genuinely wait as I spoke to my new company and they've closed the hiring and the training starts next month. I have gone through the company policy and it states no provision to pay in lieu of notice period and another clause says FNF and relieving letter (as applicable) will be processed within 45 days from the receipt date of completed no dues form (NDF) by the FNF team. Another clause states if an employee resigns and cannot complete notice will be considered as abandonment. I have asked them to issue me a relieving letter stating the same information that I have not completed notice and I have abandoned because my new company is ready to accept this as well. However, they're still stuck on no. I spoke to my Ops manager before deciding to resign and while he was trying to retain me, he asked me about the salary package that I was offered and he said that they will try and increase my salary here if I stay. However, now he has completely flipped and says that is also not possible. It can increase only next year that too depending on my performance, and they will not be correcting my salary whatsoever. My concern is, the current company has literally denied everything right from the start and I have genuine financial conditions which I cannot fulfil here. They have not looked into any of my requests, nor addressed my concerns, neither ready to increase my salary here and are not ready to relieve me even tho other company is offering me the benefits that they are not giving. Why should I stay? And what should I do in this case. Please advise. They've literally cut all the options and I feel like I'm stuck here for nothing. Thanks in advance.