IDT Prepaid Phone Card Scammed at Dallas Airport Internet

I was traveling to Mexico and stopped in Dallas to board a plane to Mexico City, right by the departure gate there was this vending machine that sold IDT Calling Cards advertising you could call from virtually anywhere to anywhere in the world. I just wanted to be able to call from Mexico to the US. I decided to buy a $10 card. I could never use it in Mexico because their "toll-free" number was always busy.

I decided to use it once I came back to the US to call Mexico and IDT told me that my balance was "low", then when I proceeded with the call they said I had 4 minutes left. $2.50 a minute??? land line to land line???. Who has oversight over these prices?

I called their customer dis service department and a very hard to understand agent said that was their rate and I had no recourse, he said he had no other number to give me to complain. I know it's only 10 bucks, but how many other travelers have been taken by hese thieves?