Hi, I would visit Howden House. It’s been a while, but am sure there are staff there who deal specifically with council tax.
You don’t need an appointment, but turn up early, as works on a first come first served basis.
When you first go in, a person near the ticket machine will ask what you need help with (I think they deal with housing and other council business aswel). You will get a number ticket for the team dealing with council tax.
From experience (be it a few years ago), I always found the staff helpful and managed to get things resolved.
I hope you get it sorted.