I would like to believe that Auto-renewal was a process that you had to actively opt-in to benefit from.
The tricky part is that it might all stem from a single tickbox on the website where you set up the policy and the form-filling page is not one which can be bookmarked or revisited. You might have no recollection of ticking the box and they will, very conveniently, have a printout of your application which shows that you did.
Proving that they 'ticked it for you' could be tricky. Not impossible but you'd effectively be accusing them of something akin to mis-selling and won't get far without solid evidence to back up your case.
If there is a way to follow the application procedure again, via their website, reach the stage where you can find an auto-renewal consent tickbox (if it exists), take a video showing it was pre-ticked and still cancel out of the page without parting with any money, then that is a start.
(Just don't stick it on YouTube until after you've got your refund!)