The Borrower is not returning the cash. Cheque bounced.

My ex-partner had committed fraud with my company and he was removed from the company for his fraudulent activities. Later his mom accepted his mistake and asked us to lend him money on credit basis so his future will not be spoiled. She guaranteed the return. The document on regular paper was created with all terms and conditions and he signed the documents as a proof that he owes us money and will be paying it on the committed date. A cheque for the partial amount was released which was due on 15th November 2015. Now he is not returning the amount stating that he don’t owe us anything. He also sent us a printout via registered post saying that he don’t owe us anything and calling him or his mom for money will be termed as harassment. The cheque was deposited once and it bounced as the account was closed purposely. Below are the details: Cheque Date – 15th November 2015 Cheque Bounce – December 2015 What is the next thing I can do to resolve this matter. I have a written document with me that says that he owes me the funds and will be paying it on time. The documents is not a stamp paper but has his signature as the proof of acceptance. Please advise.