Lied to about 10gb data plan?!

I added my tablet to my account. I got the 10gb plan for it. I asked the girl helping me about giving me an unlimited (or most available) data plan. She directed me to the 10gb and told me to ignore any texts I get regarding me reaching my 10gb limit, and that there will be no slowing down. She said that they name it 10gb, but it is really unlimited and will not slow down…

Well, the data came to a near screeching halt. Anyone experience this? Hopefully someone from t-mobile can explain what's going on