Hello, I took a international card before going to Europe for a holiday. The apartment I rented had free Wifi and the kids used it like mad from my phone. Now the phone company is charging me for that usage, although it wasn't thru them. Are they justified?
Yes, because it sounds like you guys used the phone to connect to the Internet vice the WiFi connection. If you used WiFi only, then that would not have gone through the service providers network. If you used the phone connection (as must be the case), then I think you have a problem.
Something similar to me happened a couple of years ago. You can either pay as charged or try to convince the phone provider to drop/lower the charges out of good will on their part.