I cancelled my AT&T internet service in December of 2014 and asked during the phone call to Mexico City with customer service if I could settle up any monies owed to the company. No, no no, I was told, I would need to wait for the bill. Got it, paid it, was using another ISP, didn't think about it.
Recieved another bill the following month. ??? Called customer service again, was assured that service had been cancelled, was told to ignore bill, Yadda, yadda yadda.
Same thing the next month and the following month.
Yesterday I received a bill that had gone to collections. For service I cancelled REPEATEDLY and never used.
Your mother must be so proud.