Employer Not Accepting Resign Letter And Threatening

An employee gave resignation and after service period the hod say that he had not received any letter. Now hr ask to submit resign letter and work for notice period again. The manager using abusive language and threatening of not giving relieving letter or making the letter saying that this person is fraud etc.
Even today also the manager asked him to get out without accepting the resign letter. Hr says to take the sign of hod's and Hod's say to contact hr dept. Like this they are playing.

Send a resignation letter by post with acknowledgement due and copy to the your HOD's HOD.
Do not worry about threat of his saying you are fraud etc.
If he states falsehoods or defamatory statements,law of the land will be against him
You follow the laid down procedure for resignation and company cannot hold you if you do not wish to continue.
Awkward behaviour can delay your resignation but not stop it.

Dear Friend,
How did you submit your resignation and to whom. Do you have the Appointment order with terms & Conditions regarding Resignation process.
Please give us the details then we may try to suggest.
Regards,
Manoj

Mr. Sudhakar ,
Employee need not afraid; if he is genuine on his part.
Go through your appointment letter's terms and conditions. what is procedure of resignation mentioned there.
Please ensure did employee follow this procedure ?
If employee gave resignation intimation on email to all concern person, then he must have copy of the same in sent items.If not yet mailed, then Please mail it and mention the actual date of resignation.
If only written Letter is given then take acknowledgment on another copy of the same.
And you can asked in email, on what basis anybody threat you for fraud charges in email CC to the concern person's Reporting Manager also .