Well you did better than me, I only got offered £75 for an incorrectly cancelled policy. I spoke to the guy who had actually done the deed and it appears that mistakes can happen....
All I have received in the post up to now is a letter from ASKMID warning me of fines and prosecution etc. It seems its a standard, randomly selected, off the list of folks taxed but not insured list. Shame I had it sent to me a few days after my departure abroard. My policy seems to have been cancelled on/about 9th Feb letter is dated 13th April. Is there a time limit on summons etc. as I do not want to accept anything and leave me open to the results/repercussions of their misstakes.
post off a request for all my data askmid have had on their site from Jan till May.