I have had no comments on this, so I propose to pay the discounted rate tomorrow if nobody suggests appealing.
The basis of an appeal, in the absence of a technical argument, would be that the Controlled Zone notices are still there, and I am entitled to think that they mean something. The only thing that they could reasonably mean is that I am allowed to enter that street to enable me to park if there is a vacant bay, on the strength of my parking permit for that zone. The rejection letter did not deal with that point at all.