Oh goodness banding, that takes me back.
I had it on my line for 6+ months, it never got removed, despite 30+ days of continuous connection - I think I got up to 70 days at one point. Luckily when I swapped provider from TalkTalk to BT, I got a new line and thus I didn't have the issue anymore. This was a year or so ago, I don't know if things have improved since.