Why you are delaying matter? The moment you came to know cheque was stolen you should have done that. But one thing you would like to explain to every one. You must have issued cheques after that cheque number? How come you did not know a cheque is missing . Dont you fill out cheque log sheet given in each cheque book as to dateamount and party to whom issued. Banking should be done with responsibility. Has that man access to your house/office frequently or casually, or is it that man stole it and gave to the man now claiming .Police only can resolve these issues
Yes immediately file FIR. Does that man know you? Did you ever do any transaction with him? How can you issue a cheque unless you had any transactions with him.
But delay may be adverse to you. It is lesson to all. If you give loan to even your brother just reduce it into writing even on a plain paper that why it is being given and when expected to be returned with interest or no interest. Both should sign preferably in presence of a witness. Date should be there. It is 10 minute job.
Even ask your lawyers to issue you contract note with fee settled and amount received. Now a days many lawyers take money and then dont attend case. They deny having received payment.
Dont deal with such people who are themselves doing wrong acts .How they will take care of law and your interest?
Paisa kisi ka riste daar nahi hota. No dosti in money matters, please.