data usage overcharge by cox

Cox has been claiming that on 02/25/2018 I have used 443GB data causing my account to exceed the 1TB limit resulting in an extra $80 charge on my account. The response from the Tier2 Cox representatives for my multiple inquires was almost the same: someone must have hacked my WIFI. Cox would not able to provide the IP addresses nor the time of the day when this data transfer had happened. They claim that no way that Cox's reading of the data usage would be false. Never mind that this much data with my max 200Mb/s download speed and even less on WIFI, would require someone to be by my house for at least 5 hours. My house sits on a half an acre and fenced all around. There is no WIFI coverage by the perimeters at all.

see attached graph