International charge 500$ from my account

i joined t-mobile couple of months back as i'm new to this country. I don't know the rules how exactly the billing works here. I'm charge for international charge 500$ i explained my situation to one of their associate, they told me that as concern they can waive of this bill once it got generated and he told me to call to them to make sure after couple of weeks. I called them today they are saying like that is charge you need to pay i talk to different associates in Richmond area but nothing they did. Likewise same thing happen to my friend in AT&T they wave the full amount of 300$ from their account.My suggestion is if you are new to this country please don't prefer this network they will charge you more forget about customer experience they want to charge the money that's the prime motto.