Hai:
You need to shown the proof that you have not deposited that cheque in your bank account, for that give the bank statement xerox copy showing that you have not claimed the refund.
the following information is required to be furnisehd to the concerned ITO.
1. A letter stating the you have lost the refund cheque.
2. Self attested affidavit on non judicial stamp paper of Rs.10 or above stating that you have claimed the refund.
3. Xerox copy of bank statement.
4. Assessment copy.
5. PAN xerox....
it will take time to get back the refund again....