Ah Maw it is so very upsetting, isn't it? Somehow just seeing "Dear Mr....." on a current letter brings the loss so much to the surface again. My DH was continually brought low by such mail addressed to his parents after they'd gone. When his DF died, his DM went into a care home as she was wholly unable to care for herself. We therefore wound up all DFiL's affairs, all the bank accounts, utility bills etc, and sold the house.
We live in the same area, and use some of the same utility companies, and one of them in particular simply could not get their heads around the fact that there were two Mr B's on their books and could not get their records straight, no matter how many times we rang them or wrote to them. So for around a year after DFiL's death, all our electricity bills were addressed to Mr <my DH's name> (dec'd). You can imagine how distressing it was for him - and me - to repeatedly see post addressed to him in this manner 