@br00t4c My sister just had this kind of problem with Verizon.
She had someone on her family plan pay off their phone and leave the plan. Verizon continued to bill for the now-paid-off equipment for another 3 months. In person service couldn't help, customer service by phone wouldn't help. One of the customer service by phone sessions went so infuriatingly badly for all involved that the in-store rep probably ended up fired for what they said to the phone rep.