I missed the thread that stated his router is overheating. That said, you have one or more of the following issues that may be eating up bandwidth:
1. Software updates (like windows, game or AV updates) taking place
2. Torrent server still active
3. Virus/bot running malware (like a mail server or ddos bot)
4. Possibly you wireless modem has a hijacker using your wifi (depends on type of wireless modem you have ( wifi router access or hotspot?)
5. Software backup/sync to cloud service running (Dropbox/one drive/Box/Gdrive/etc)
You have a little detective work ahead, but like mentioned earlier I would start with task manager to see what is active. Then try installing some tracking software and running your antivirus.
I was watching the task manager as the latest data surge occurred and there was nothing unusual.
1) I set all software to update manually and am running a minimalist Windows system. There is little to update aside from Windows which I do manually.
2) I do not use any torrent on the computer.
3) It does look like malware of some sort.
4) Physically I am about a quarter mile from any other house.
5) I have no cloud services on the computer like dropbox etc.
I do notice a correlation between running certain coin wallets, like xcn, and these surges but the wallets are widely used and not likely infected. The data surge takes into account any possible useage by wallets. I have been using coin wallets and know what sort of traffic they cause.