Employee has resigned without any notice period - Can we stop all his clearances?

I am working in Small Scale industry as an HR manager and I just want to ask in my company an employee has resigned without any notice period, whereas in his joining letter is mentioned before relieving he has to give 3 month notice period. Can we stop all his clearances? or other methods to handle this plz suggest me.

Dear Friend,
What your appointment letter clause says look into it, many companies do the practise of recovering his notice period days and will make his clearance.