-- You should have received the notice, in the notice what does complainant say about the cheque and liability ?? Has he stated that in order to clear the liability arising out of so and so supply you issued this cheque or he is attaching some other liability ??
-- If this is not mentioned in the notice, then surely it would be mentioned in the complaint, a copy of which you would have received ?
-- Now assess the situation from pure evidence point of view,
a. Any evidence that you issued the cheque in advance ??
b. Any evidence that the cheque issued for the same transaction ??
c. Any evidence that you returned the material after rejection ?? (**)
d. Any evidence that complainant received back the rejected material ??
e. Any evidence that he acknowledge the cause of rejection ??
If you have solid cause of rejection and if you have intimated to him in writing, before the cheque got deposited and if you have his acknowledgement, then even you need not return the same, it is his responsibility to collect back the rejected material.
Now the worst part, even if you have all the evidences as suggested above, you have to contest the case, so bad.