Appealing to Council Tax Valuation Tribunal Service

Hi
Does anyone have experience of this?  I requested a S.13A write-off in July ‘22 and despite lots of chasing, have only just had a response turning it down.  My request was on the grounds that the client claimed CTR late and accrued a debt of £590, which he wouldn’t have had he claimed at the right time.  They are recovering it by deductions of £16.75 pcm.  He has serious MH problems so it was ‘natural justice’ request, though I did provide a financial statement.  He gets UC with the LCWRA element but no PIP.  Cherwell District Council’s response was to address only affordability, saying he’s paying too much for his broadband.
So my question is should we appeal to the Valuation Tribunal Service and if so how should I approach it?
Thanks

If you client has serious mental health issues have you considered making an application for the severe mental impairment exemption for council tax? This can be backdated and might take care of the issue

I’m sure he wouldn’t qualify for SMI, it’s more depression and motivation-related.