I feel for you. I too and having Supanet troubles. I think they might be in severe trouble and trying to claw at money by any means. I have had 3 letters from Daniels Silverman. I however don't share your faith in that company. Daniels Silverman have said they are sending someone to my home address to "discuss impending legal action" . As the matter is in dispute, they are acting contrary to Section 40 of the Administration of Justice Act 1970 'in that they are intending to cause alarm and distress’
Anyway, my Story is different to yours. I was with Supanet for 14 months. Minimum contract was 12 months. I cancelled because of terrible speeds and latency. It was unusable for my needs.
Half way through this time they changed their Terms and Conditions to say that if you cancelled within 24 months there is a £39.99 cancellation fee. I was never made aware of this. Apparently they sent an email. I have asked other people, and it was the last line of a junk sales email sent to all customers. Not to the email you signed up with, but to the email they gave you. Since then they have written to me on several occasions demanding this money (which has now risen to £85). Not once did they manage to write to me regarding any changes in T&Cs.
I don't think they should be able to get away with these bully tactics.