Hi,

You can wait till the site's owner Robbie sees this, or, the quickest and easiest way is to log into your Paypal account. Click on Activity, then look for the payment (it'll be for Fantaseum LLC). Click 'Manage Fantaseum payment' and you'll be able to cancel it from there.

If this doesn't work for some reason, I suggest sending a PM to Robbie. Unfortunately he's the only one who can deal with this. You're still under five posts which means you'll have to make one more comment before you can use the PM system (an anti-spam measure). If you reply to this comment, that'll get you to five, then you need to wait up to an hour for the server to update, and then you can PM.

This is Robbie's profile.
https://www.cartographersguild.com/member.php?u=567