Then in early February a BT bill arrived, expected to be the final one. Instead, it not only did not refund payments from mid-January onwards, it also billed up to early March. The services at BT had not been cancelled, despite my relative having received a letter from BT advising they would be.
So I took up the case for my relative (with their permission of course) and rang BT (customer options team). On checking his systems, the agent was adamant that my relative's service had not transferred to Sky. I told him my relative's telephone calls and broadband usage were being logged in my relative's My Sky, and he was not interested. He said Sky had not processed the transfer correctly, and therefore Sky needed to sort it out. He said if he processed a cancellation, my relative's phone and broadband would be cut off. Since the man would not listen to reason, I had no choice but to ring Sky, knowing what the outcome would be.
I rang Sky who confirmed the migration to them had processed correctly in mid-January without issue. He checked Openreach systems to confirm it, and he even apologised despite it not being Sky's fault.
So I rang BT (customer options team) once again. This time I was passed to someone who was willing to listen to me, he checked Openreach systems and confirmed that the migration had taken place in mid-January and that my relative was incorrectly being billed by BT from that date. He wrote notes for the offline team and I think (and hope) that it will now be resolved.
I accept errors in the migration process can go wrong, but the first BT guy was a nightmare. Completely unwilling to accept an error could have occurred on BT's side and steadfastly blaming Sky when it was not their fault at all, resulting in far more hassle and frustration for us than there needed to be.