Most insurance companies will insist on the full years premium to be paid if there are any claims in that policy year. So while technically you could cancel it the day after, there wouldn't be any point as you'd be paying for the cover anyway.
This particular case is odd, in that it seems the insurance company is claiming they are not eligible for cover, but they had an accident during the time it took to decide that you were not eligible, so you have a claim outstanding (and so are due the full years cover) but are not going to benefit from the rest of that years cover. That's seem a bit unfair to me. To me if they are going to charge you for the full year they should provide cover for that charge! If they can't then there must be some middle ground where they didn't have to charge you the full amount simply because you were unfortunate enough to have had an accident while you thought you were covered. But without knowing the policy you're with, and the small print for such a scenario (if it is covered), it's difficult to say for sure. Technically they could be entirely within their rights to charge what they have charged, harsh as it may seem.
Btw this is assuming the reason for non coverage was unforeseen by both sides. If information was deliberately left out then that's fraud - but then in that case I would have thought the insurance company would have stated they are not liable a while ago rather than letting it drag on like this.
However, OP, I'm also having difficulty following your posts. I hate to be the grammar nazi but you'll need to organise your posts better if you want the best help. A timeline of events, with as much detail as you are willing to give, in full sentences with paragraphs, will make it a lot easier for people to follow what you are saying and advise appropriately, rather than try and guess what's going on, where we might give out wrong advice.
Ultimately, for a complicated case like this, it's probably better to seek professional advice.