Data usage inaccurate

I have logged queries that my data usage is incorrect , as soon as I load 2GB bundles they used totally within an hour or 2 , the PC is idling with no updates no apps running in the background and no cell phones connected to WI-FI, even after powering off the device usage is been used. I called the call centre and I am told I cannot topup my contract with a credit card, however I have done this coupler times and it works. I really need help