Keep evidence of your orders to disconnect service with the phone companies. Make the evidence part of your records that you save as long as you do your vendor invoices. At a minimum, you need an order number, date you called, and who you talked to. Better: emailed acknowledgement of your order number, disconnect due date, and a follow up confirmation number of your completed order.
Next, watch the next 1-2 invoices from the vendor. Make sure the services disconnected come off the invoice.
Lack of follow through. The phone companies loose things. If you don’t have evidence you can document, you can’t seek a retroactive refund, back to the date you requested a disconnect. It’s money down the drain to you.
Issues like this happen. The error can run for years on end before it’s caught, with no way to recapture the money you’ve lost. So, what was a $63/month disconnected service…after five years is $3,780…and this was just one small item.