Hello, I am Keith, one of the experts on Just Answer, and pleased to be able to help you with your question.
Benjamin Franklin ones quipped that in life there are but two certainties, death and taxes. Here is the Gov UK web site information on exemptions from council taxes:
'4. Discounts for disabled people
People who are severely mentally impaired, and live-in carers who aren’t family members, aren’t included when working out Council Tax.'
It is therefore possible that your special needs son should not be included in the council tax computation and that you should be receiving the 25% discount for single occupancy. If you are not receiving this discount you should claim it from your local council explaining your circumstances.
The full gamut of the advice can be found here:
I do hope that my reply has been of assistance.