First off, let me point out that I have nothing against you, Aviv, or the person he accidentally gave your key to. So, please just take what I am about to say as constructive criticism, which is all it is meant to be.
Basically, I think people should just buy their own key. Really, it's easy. Don't have a credit card? Go to the nearest Walgreens or other store, and BUY a Visa Giftcard. It can be used JUST like a credit card, and you can pay for your key with it. It's not hard at all to do, can be done all in the same day, and is actually safer than using a credit card, because there is no threat of theft like with a debit card or credit card.
If your parents don't let you use a GIFT card with your own money, then you have unfair parents.
Anyway, don't take this the wrong way, I'm just trying to say that it's really not a wise thing to go around buying keys for other people, as something like this could occur, or worse, a third party may somehow get a hold of the key.
I am not trying to say anyone stole keys.
This is mainly a post for future reference, in order to help other people from making the same mistake.
I hope this matter gets resolved so I can see both you and the other person on my server. I know who the impostor is and he is not a bad person as far as I know, and he said he noticed that the number of the Blockland ID or whatever wasn't what it was supposed to be.