VRM means vehicle registration mark - ie your numberplate. There's no need to cover this up, it's on display to the public all the time.
To me this looks fairly straightforward, if you were "parked outside their patient/client’s home address" then your pass is valid. You should write a fairly simple challenge and include proof that you were parked outside the patient/client’s home address, and the Council ought to cancel the PCN.
Complaining about the Warden is also possible, but it should be a completely separate process to appealing the PCN and would best be done once you've got the PCN cancelled. Mixing the two processes up is likely to confuse matters.
