I had similar issues with BT not that long ago. My dad died 2 years ago, all the bills on the house we lived in (with my mum) were under his name. Day after he ded I contacted all the companies, paid off last bills and transferred all accounts to my mums name. Everyone managed, apart from BT. The first bill was fine, addressed to my mum, no prblems, But then the next three were addressed to dad again. I paid the first one, put it down to a mistake, and called BT to ask them to not send any more letters for dad. The nest bill arrived, addressed to dad again. I got a bit miffed, called them up again and was told it was sorted. The final bill arrived for dad again (we were changing line providers this time) I refused to pay. I called BT again and said I would pay when the bill was addressed to my mum (who they confirmed was the name on the account!) Red letter turned up for dad, and then bill after letter addressed to dad moaning about how he hadnt paid the bill. In the end I sent BT a letter, informing them of dads change of address to 'plot no *, adult section, crownhill crematorium' where he was buried, but pointed out that since he had been dead some 12 months, chances are they wouldnt get any response, but maybe they could employ the services of a clairvoyant if they wanted further contact with him. A week later I get a very apologetic phonecall from someone at BT head offices, saying they were really sorry, no idea how this mistake had happened, and as a gesture of goodwill would write off the bill!
Sometimes being sarcastic is all that does work!