You have posted that written condition was that “if candidate is failed to join on the given date, the offer will be cancelled.“
Candidate has failed to join (despite having signed a letter copy of which is not kept by or given to candidate) by this date, so the matter ends.
The reason quoted by you for not joining is “on the date of joining he had very harsh communication with both of the employers so he decided not to join.”, so the matter ends.
“When he declined the offer evry thing was orally communicated over the phone.’;, the matter ends. ( Keep the bill of phone calls safely.)
If it is not written in offer letter or the letter signed by candidate that if the candidate does not join he is liable to pay a penalty of Rs…………, the matter ends.
If he is being threatened he may record the phone calls and approach his lawyer/police.
If this HR calls again the candidate may narrate the bad conduct of company on date of joining, and that he has already declined to join on phone on dated………….to ………name of company personnel…………and put the matter on “Shut Up Mode”.
If the candidate is getting tormented for none of his faults why is he tolerating the nuisance?
If he is not able to understand the matter or handle the matter, he may approach a lawyer/police/trade union and let the lawyer handle the matter.
If the company has issued/or issues any communication/notice in writing, he may approach a lawyer/police/trade union and let the lawyer handle the matter, and put the matter on “Shut Up Mode”.