The winner of my giveaway blocked me when I added to give the gift

Re-roll and blacklist.

Make a screenshot, provide it to the SG staff and have a reroll.

Well I mean I cannot add him back and he's not on my add list anymore.... I'm pretty sure he blocked me!

I think you can ask support for reroll. Create a ticket, as a reason choose "Unable to contact through Steam or Email".

first be sure to go thru all avenues of gifting before making a support ticket... Send them an email with the key/link if it is one of those.. if it is a gift item in your inventory, there is an option to send via email as well. Some people block random steam adds or just ignore them.

Lol, that is fun!

wait 7 days then contact support for a reroll. also provide that screenshot & i would blacklist them for future giveaways.