There have been several reports of doorstep callers saying the householder is entitled to a refund on their Council Tax due to a change in banding. The caller claims to be an agent of the council. Although the service is 'no win no fee', successful claimants are charged around a third of any money received.
If you are concerned that you may be paying too much or your house is in the wrong Council Tax band contact your local Valuation Office Agency (VOA) on 03000
501501 or visit https://www.gov.uk/council-tax-bands where you can check you council tax band free of charge.