You pay council tax on your address, not on an individual basis. So if you moved house and didn't tell them, they quite reasonably would have counted the payments towards your old address, not your new one.
I did tell them, the person I told said I could keep my automatic payments going, which I did for a year before they said I hadn't paid a year on the new address and had overpaid a year on the old address.
They then denied knowing that I had moved address, but didn't have an answer to "then why have you sent me a letter (to my new address) saying the payments for the old address should be refunded if you think I still live there?" (they literally denied knowing I had moved after sending the letters).
I appreciate that involved human incompetence not just a poor IT system, but a better system would have made the updating of me as a person paying council tax from one address to another seamless, then it would have flagged the problem sooner than a year in, and then it could have crossed my "debt" with my "overpayment" rather than passing it (in what I assume was another human mistake, but again allowed by the system) to a debt collection agency.
