Cell phone company charging me $20 for a game I didn't buy?

[I <3 M&Ms]

So my cell phone company (AT&T) is charging me for using "game mobile" or something like that. I haven't even bought a game! I played some of the demo games, but they have always been free. I went and talked to the lady at the AT&T place and she couldn't even tell me what game I bough. Then she said it was tetras, but I bought that game a year ago and I only paid $5 for it. Then she went back to saying she didn't know what the game was!

Any ideas about what I can do?