Hi Statshine
How cruel, after all you have achieved. So sorry to hear this and I do wonder if you can contest it, whether you can have assistance to go through the case and demonstrate how its arisen. There are many experts out there also that can help guide you through this process.
There is an organisation called step-change, who are there to help people manage debt, and help deal with the entity you are in debt to. I think it would be well worth you calling them, even if they can’t help they could also possible signpost you to a body that can help.
Good luck with this, its just more of the same from him isn’t it and given your circumstances if you speak to them, they could also offer you their rules for navigating this, and the path to take to challenge it?
warmest wishes
ts