Not giving Bonus which deduct from my salary and part of CTC

Thanks to all in advance for your reply. I am working in Pvt ltd company since September 2021. When I joined, they just gave me an offer letter that did not mention any notice period. They did not provide any salary slips every month. I have my salary break-up letter with me on the company letterhead. First of all this company did not give any leaves (15th Aug, 26th Jan or 2nd Oct). If they give leave on any particular day then they deduct the pay. If we did not take any leave still they deduct the payment and add in yearly bonus pay which they are supposed to pay on Diwali Month. Now, I got another job and have to join on 12th September 2022. So, I gave my resignation letter through company e-mail ID to Company Director and Company HR and informed them that I will serve 15 days notice period. Now, they are telling me that they will pay me a bonus only if I will be working till the Bonus payout day which is not mentioned in any letter. Moreover, If I want an August(2022) month salary then I have to work a minimum of 10 days in September(2022) without any payment otherwise they will not give me an August(2022) month salary as well. I request you to all please suggest to me what to do because I do not have a strong financial backup. Please help me