It sounds like you somehow did an 'account switch' rather than simply changing tariff, so you got a new account.

I believe that can happen if you pick a new tariff from the 'Get a quote' webpage rather than changing tariff through your account on the 'Renewals' page.

So it would be a bit like moving house while keeping supplier - moving out of your house and back in again all on the same day. The computer wouldn’t be bothered at all that your ‘new’ address was the same as the old one.

@Firedog  didn't that happen to you recently? IIRC you did manage to get it cancelled and stayed on your existing account.
(PS. Lightbulb moment about what may be going on with my own account as reported elsewhere).

As for the new balance I dunno, but is it perhaps actually saying -£2475 debit?
A minus debit is a credit.

Yes! And of course it happened just before an extended bank holiday, so I had no way of cancelling the change until the new tariff had been in place for a few days. It was quite simple to cancel - I was still in the mandatory 14-day cooling-off period. I called 0800 012 1232 and got through straight away to a very clued-up agent. 

There is one hangover, though: the new account that was set up by accident is still there, and I’m required to select the right one every time I sign in.

Hi @ArchieThom,

I’m sorry to hear this.

I can see our forum volunteers have already given some good advice here. This definitely sounds like it has been done in error. I’d advise contacting our Support team so that they can look into this further for you. 

Please keep us updated.