SMI certificate & co.tax

Hi there, when I lived in Brighton my doctors, who knew me well, gave me an SMI (Serious Mental Impairment) form (2013) which meant I didn't have to pay council tax. I have bipolar disorder, Now I've moved to Bristol and a GP who's never met me, who didn't ask any questions, and with whom I am a temporary patient (and who possibly didn't understand what the form was for)  ticked the box on the form (2023) saying I do NOT have an SMI. I don't know if I've made a miraculous recovery and just not been aware of it -  if anything my mental health has got a lot worse (subsequently been diagnosed with C-PTSD and am mid-assessment for ADHD)

The criteria for SMI (in Schedule 1, Paragraph 2 of the Local Government Finance Act 1992) is 'the person has severe impairment of intelligence and social functioning (however caused which appears be permanent).' If this was deemed to be permanent before, how did it then become not permanent? 
At a cursory glance at the brief, woolly guidance the SMI is for people with Alzheimers and stroke etc, however plenty of people with bipolar get it and at least one council lists bipolar on their SMI criteria (it just seems quite patchy around the country) 

I thought the SMI was just a question of confirming my diagnosis, I didn't realised I'd potentially probably have to provide more information in order to meet the criteria for that judgement, and neither the council nor the NHS were transparent about this. 

My financial situation is my number one stressor affecting my mental health, and due to this GP's box ticking I'm now liable for the full co.tax debt (thousands) I ran up when I was too unwell to open my post or deal with my affairs. I am still with the Brighton GP as well as temporary patient in Bristol, I don't know if Brighton reissue it whether Bristol council would accept that or if they require it to be a Bristol GP - it's a clinical opinion rather than geographic, but still. 

Is there anything I can do here? Thanks, and apologies for the essay.