[ZombieBerry]

We really cannot help users with these types of issues. The best people for you to contact would be your service provider. Especially if it involves billing/data usage.

Is it possible some third party app is using your mobile network instead of WiFi? Probably. You can also consider, that you have been really interested in voIP calling and unless you are connected to a WiFi network, you will be charged for the data sent/received. I suppose you could also disable Network Services but some apps need that connection to be there.

Perhaps you need to upgrade your existing service package to another one? Contact your provider will certainly help you in either case.