A manager rejects the resignation of an employee. What can he do?

Dear sir/madam,

I received an offer letter from another company and the same day I forwarded my resignation letter. My manager went on emergency leave, hence I sent my letter by email.

20 days have passed and he still did not acknowledge my email. When he came back, he was furious with me for submitting it and adamantly rejected my letter.

He even said that I can go to labor for all he cares.

Can you please enlighten me on how I am going to proceed?

He does not want to talk to me in a civilized manner.

Appreciate your advice.

Thank you!