Wrap it in aluminum foil.

Whilst this sounds a lot like a foil hat joke, that's literally the easiest way to wrap something in a conductive material cage (i.e. a faraday cage).

If you don't want it to look ridiculous, put it inside a box whose inside has been lined with aluminum foil.

Mind you, personally I too would just cancel that shit, but the option is there to carry on using it whilst blocking its radio emissions.

This was fiber, if that makes a difference. I asked the install guy, he called his boss, because no one had asked him that before. He told me "no, it's not allowed". Also, I tried plugging the patch cable directly into my own wifi router and nothing.

It's a "costs extra feature" for the customer. But, they have access to it regardless of whether it's "turned on". It's never turned off for them. And, if that puts me in tin-foil hat territory, so be it.