Need justice for work done

I have worked for a Client for 2 years  
I am a Developer i Have developed a Software for Him 

But the Client is Irrational 
He demands full Refund after the work has been Completed 

He did not sign an agreement or he has any receipts from my end

I was threatened by him and was forced to give a blank cheque  

But I want to Fight for my work 

and I dont want to pay him back coz i have worked hard for the project 

I have the proof of work done for him along with some of his instructions  and his communications

But I fear he will deposit the cheque and raise a cheque bounce case on me 

Please suggest me how to fight back 

<< Client has never signed an agreement nor has any receipts that he payed me >>

dont worry , go for FIR  to police station tell them everything

check bounce case cant be run only by getting blank check there are too many thing to prove for eligible and legal transation , search you will find many judgments for that

before taking any work, make sure to explain period of work ,and other terms ....

Firstly, you should write to him under a registered post asking him to return the blank cheque held by him which is illegal and not to misuse it for no reason, simultaneously you should write to your bankers to stop payment on  the particular cheque if presented for collection, you should have a copy of this notice to bank in your possessions, after that if he proceeds with cheque bounce case, you can  use these evidences to defend your case.