The council must be informed, within 21 days, of any changes to liability or entitlement to discount or exemption. If notification is not received within the time limit the council may impose a penalty of £70. This will be added to your Council Tax bill.
If you get a penalty and think it’s wrong, you should tell the council why as soon as possible and ask them to change it. You can also ask a Valuation Tribunal to look at it again within two months.