/invade
Hi. You need to get in touch with a TA about this. Ideally you need a screen shot as proof, but since your not the only one that's been ripped off by him in the past 24 hours you might not need it.
As a note so none of you get ripped off again, try and keep all your purchases on the forum - if you do decide to buy/sell something while in game make sure you take a screen shot as proof in case it goes tits up.
Good luck with getting this sorted.