Just make sure that you have officially communicated the notice. Take a copy of the email and save it as your personal email or so. Tell the manager that you fully intend to leave and your last day is (date). Send an email after the conversation.

Take a backup of all your pay slips and any details such as tax documents. Serve the notice period truthfully.

Talk to the other company where you going to join and explain the situation. They will likely accept the paystub and your resignation letter as proof of your employment and resignation. Formally request a relieving letter saying that you worked from this date to that date. Never mind if they won’t provide one.

It is up to the employer to determine if they want to start the Knowledge transfer or just drag it out. This is a usual tactic to get you to stay under unfavorable circumstances. And never accept any counter offer, as it will be bad for you, as they can fire you on their own terms once the replacement is found.

Also, remember that the law is on your side. Bonded labor is illegal and you have full right to leave a job you don’t like.