[tsac]

Normally the phone does not send or receive any data unless an APP is checking a server or some other thing. BBM is nothing more than texting and unless you have an app running like facebook which checks for updates there is no reason for the phone to be doing anything.
Go to the settings, data services and turn off the data access to the internet to see if is clears up the problem.
As for hacking, unless you are receiving a lot of emails or text messages because you gave your id or cell number out it generally is not something to worry about. You will get a few call scams and if you don't answer them they will most times not call again.

I would check all your apps on the phone and after doing a backup using Blackberry Link ( free at Blackberry.com) delete them one at a time and check usage. The one causing the problem will show up.

Good luck