Tell them you didn't know you were roaming and ask if there is a way to keep the phone from roaming. We both know there is, but it makes you sound a bit more credible. Don't yell. If you start to lose it a bit, catch yourself and apologize to the person you are talking to telling them out is not them.
See, people think it is ok to yell, scream, and talk down to customer service. So most the people they talk to are assholes. If you be the kind, persistent beggar, they will go out of their way for you. I know, I do tech support that was forced into being customer service instead. You yell, they don't jump. Scream you are going to cancel your service, they just transfer you to another department.
Be nice. Complement them. Day stuff like "you have a very pleasant speaking voice" , "you are so kind", here is the best one.. "the last person i spoke to didn't seem to know what they were doing, but you seem right on top of things
I have gotten Sprint to send me a new phone for free, let me buy out my contract for $25 when it should have $125.waive every upgrade fee. And allow me to buy out my contract for $100 when i did not qualify to do so, and it was still discounted to $100 from $125.

it does work if you know how to play the game. Sometimes it does take a few tries though.
Just because you're paranoid, doesn't mean they're not after you.