One of my giveaways glitched and duplicated :[

You could have deleted it yourself before it ended.. now you are screwed yes :p

Easiest solution: Buy the game again and give them to the winners and forget about it :p

I don't know, I would just wait for support to reply

Just message the person and tell them. Points come back, and they didn't lose anything non-replenishable by entering the giveaway.

I chose a random winner, send the gift to that person then sent an email explaining the situation to the other person.