Resignation letter rejected, OTY

Please advice. We work in a call center company and as agents, we are required to meet targets, team targets. However, it has been a year since we are rendering overtime, mostly unpaid. We already raised this to re calculate as this seems we are understaffed. They are now adding people to the team but since overtime is unpaid and this is not the agents fault, we feel like thia ia unfair. I submitted a resignation letter but was rejected saying this is unfair and unprofessional without reading the content. She says that she needs three months to train competent people and until then we cannot resign. We also have leave credits but since this is not paid if unused, we try to use it but our planned leave was unapproved and most will just be absent if really needed to. They are saying that the max number of leaves has been used up. As i feel like im not growing in this company, i wanted to resign properly and would render the 30 days required and would like to be out asap as I have already submitted resumes to other companies. what would be best to do since the Team Leader wont accept the resignation and would not do anything about the unpaid overtime, unused and unpaid leaves? We fell we are being treated unfairly. Thanks

If wala naman sa employment contract na u have to render a 3-month pre-resignation service kasi kung pipilitin ka nila, involuntary servitude na yon. Well, kung di nila ibigay ang ang monetary benefits mo, go to DOLE and file for money claims.