How to contact a winner of my own giveaway

The message was left on the profile of that user.

Don't hurry. You have 7 days to sent the gift/key, the winner has 7 days to activate the game and mark it received.

i think you will find his email on the winning page , they show his username and his email

That's the first time I'm hearing about such a thing. Are you sure this is the reason your account has been blocked ?
For contacting a winner, you can also post something in an old GA of him (if this user made GAs), or send him a direct email.