It's the VOA that determines Council Tax bands in England & Wales, not local councils. So if you actually believe that there's any chance that your home is in the wrong band, start here:
https://www.gov.uk/challenge-council-tax-band
If you're in Scotland though, start here:
https://www.saa.gov.uk/council-tax/council-tax-proposals/
Affinity Tax Consultants is a trading name of Affinity Sales and Marketing Ltd. It was set up 17 months ago as Warranties Plus Limited but changed its name to Affinity Sales Ltd in August last year. (The "and Marketing" bit was then added to the name in March of this year).
It's run by a 59-year-old guy called Alan Prior, who's also the sole director of Unity Consultants Ltd (which doesn't seem to have any form of web presence), which was set up 9 months ago. He previously set up a company called Spaciia Limited in September 2015 but applied for the company to be dissolved just four months later (which could well be explained by the Insolvency Service action referred to in my link below).
The addresses for the registered offices of Mr Prior's companies suggest that he's based in the Brighton & Hove area. In which case there would seem to be quite a strong possibility that he's the same Alan Prior (right age, right location) who was banned from holding company directorships four years ago:
https://www.theargus.co.uk/news/13599350.publisher-alan-prior-banned-from-business-over-tax-failures/