Mine is with SmartParking too and my research brought up the same opinion of them when challenged. It's two weeks today that I sent in my appeal to them which I think means that they've just folded after receiving my appeal. Fingers crossed anyway.
I had to appeal as I received a notice to keeper which as it was in England meant that I could be held liable regardless of whether I was driving or not. I wasn't but that's another story, you couldn't see from the photograph on the letter but when I appealed on their website you could see their 'evidence' which was higher resolution. It wasn't even me driving not that it's so relevant in England (it is in Scotland).
In any case, charge not an accurate pre-estimate of loss or absurd or unconscionable (take your pick
if you should hear more).