PotatoSalad, I mean either that or he bought you that many t's. I think you did. because 600 divided by 30 is 20. 500 times 20 is 10,000 T's which is how many you're missing. If you didn't hack it, then Randomize fucked up.
I refunded some T$ I bought many many years ago and the same thing happened to me. I somehow got in touch with Randomize via email and that's how I figured out it was because of that.
But yeah that's exactly what it is. Whoever was behind the buying T$ somehow had it cancelled and so it's being taken out of your account.