What is the woman’s problem?

W: You’ll never believe what happened to me today. I got my phone bill for this month, and it’s over $100! The worst part is, I didn’t make all of the calls. There’s a bunch of extra long distance calls.
M: That’s unusual. Did you remember to pay your last bill?
W: Yes, I always pay on time. And the only time I make long distance calls is to speak to my sister in America. I’m on the Internet a lot, but that’s a flat rate every month.
M: You should call the service provider today and see if they can sort out the problem. They can probably remove those charges from your bill.