This may not be relevant in your case, but when I wanted to change ISP, they said I would need a new provision, as there was no phone line connected to our house (despite the fact that I was talking to them from my house phone).
It turned out that Openreach still had the phone line registered to the old house name, despite the name change having taken place 6 years ago! I'd also previously changed ISP from BT to John Lewis (i.e. Plusnet), but that didn't highlight the issue.
A quick phone call to my current ISP sorted the problem. Even OR catch up eventually!