At that point I discovered that I was right back where I started - PlusNet had never actually closed my account. It had also charged £21.99 to my credit card instead of the £18.33 they claimed I owed. And they had added my card details to the unwanted account, ready to grab any money they wanted in future.

Although I can now move to my new ISP, the final slap in the face is that I must cancel my PlusNet account again, and that means another 30-day cancellation fee. A call back into PlusNet resulted in a promise to look into the matter and get back in touch. There's been no word since.