Disappointing Technical Service

I have had a data contract with Telkom for +6 months. In September, 20 GB depleted in a day and no one can offer me a reasonable explanation as to how this can happen especially when out of the 3 devices that connect to that router, only 2 were connected and it happens to be WiFi cameras which use the app on my phone. My phone still had 20 GB but my home network didn't.