It's for council tax.

I've just received a final demand for over £1000 despite having paid every bill the council has sent me. They usually send a letter every month, which I have paid at the town hall as soon as it arrives. This month nothing came through (no bill and no reminder) and today a final notice landed saying I had to pay the entire sum within 14 days. I work long hours and my council don't have any phone lines open after 5pm. Can anyone help me decide what to do next to sort this out? Edit: bill is for council tax