Doesn't matter if your cousin used his work or not.

You didn't state that in your thread. You said if "completed within few hours" which he did. You were the one not responding to him when he completed it.

Lets say you were in the exam hall sitting for a 2 hours examination. You finished within 2 hours. The examiner collected everyone's paper but purposely didn't bother to collect yours, and only came to collect yours 30 minutes later. Then he said "You're suppose to finish in 2 hours, but its already 2 hours 30 minutes now" you flunk your exam. Who's fault is this?