My company took my 10th original marksheet but I want to leave but they are asking more money.

When I joined on Feb 2021, in my offer letter it was said I will get 16000 take home salary and I have to work for minimum 1 year and if I break the bond I have to pay 2 months salary or training cost and they took my 10th marksheet as security. In lockdown period in WFH one month they disabled us from working and told to come to office then I got 20 loss of pays due to lockdown travel so I should have got 8 days salary but they mistakenly sent full 16000 salary and later told that we will cut it in 3 months(4000 rupees/month). And now after 6 months I want to resign due to higher studies so I told my team in charge to hold my August salary and I will give another 16000 from my end but now the HR are saying my real salary is 17200 and August months salary I would recieved 5000(due to previous mistake full salary) so now I have to pay {17200+([deleted])}. We never recieved 17200 salary in this 6 months also we recived 16000 salary only 1 or 2 times otherwise we only recive 6000/9000/12000 like this never full salary I come from very far after this room rent/food how can I save this much money from this salary. Can not even support my family. I am financially broke please suggest me what should I do, I sent the resignation letter my team in-charge approved that but I am stuck on this marksheet and payment issue please suggest me what should I do?