I once set up a 1 month hotspot with Verizon when I moved into a new place that didn’t have internet yet. After the month, I returned the hotspot to the store and they told me I was all good (in writing too!). Then I started getting monthly bills that I couldn’t cancel online or over the phone. I repeatedly went into the store and they told me it was a billing mistake and they’d fix it. Eventually they sent me to col…
This was modus operandi for Comcast as well, along with continuing to bill you for service at an address after you'd canceled and moved off the property. IIRC one older woman went to their local offices and started whaling on things with a hammer in response to this.