So, it was a match day?
Nothing on their website fixture list...
Again, the website says that stewards are present on match days.
Presumably there weren't any around to advise you not to park there. That's their fault.
Anyway the usual advice here is not to appeal and just to wait for a "Letter before claim".
If one arrives, come back here for advice.
Ignore all the threatening letters they're going to send in the meantime, but file them away.
Also read up a few other threads on the forum, so you know what's likely to happen.