Data usage alerts injecting code

Hello

I recently started receiving alerts as to how much data I had used, 85% of my monthly allowance. This is not an uncommon event and my first alert was an email. I looked into it, found everything to be normal and as we were very close to the end of the month, it wasn’t much of a concern. 

A few hours later, on a windows PC, my browser threw a little pop up ad telling me the same 85% data usage alert. The only interaction This device had with Cox was joining a WiFi network run through them. This is a big problem for me. I had already received the alert and did my part. I understand you want customers to be fully aware of their data usage and to ensure the right person gets the notice. This pop up ad is my ISP running code on my computer, and that is not something I agree to. If there was any consent I gave to allow cox in any form to execute code on any of my devices, I would really appreciate a link or pointer to that document so I can review it and find out what my options are to never allow this to happen. Can anyone explain how this is happening on a detailed, technical level? I would appreciate a web developers perspective on how this is being executed. 

Is this Cox running code on my devices? Can I disable the ability for Cox to run code on anything I own? Who can vouch for the security of the code you are running on my device just by joining a WiFi network? All I did was have a windows PC on WiFi and you get to run code?