It may take a bit of time to go through but if you think there was an error in information or such for the donation start a PM with @Fredy explaining the situation.
If you've bought it while being on the server and haven't left since buying it, try re-logging onto the server so it checks out your purchase and can give you all your Premium perks, if you've re-logged and your Premium perks aren't there then I suggest contacting @Fredy by using the PM function on the forums as @Janice mentioned.
Also, make sure you provide proof of purchase. Just in case Fredy cant finds it himself. If worse comes to worse then you might need to purchase VIP using in-game funds instead. Or by all means, buy it again which I doubt you will do.