Ask your local council in writing for the reasons for its decision and request a review or appeal under its Council Tax Support scheme. Include relevant evidence, such as income details, rent information or documents explaining a change in circumstances, and keep copies of everything. If you remain unhappy, you may be able to appeal to the relevant valuation tribunal; in England, this is generally the Valuation Tribunal for England after the council has replied or failed to respond within two months. Check your council’s instructions and the official GOV.UK guidance, as procedures and deadlines vary across Great Britain.