@stamfordman, surely ****8337 has been paid, there's nothing outstanding as far as the letter is concerned.
'As we have received full payment...'
Anyone can pay, IMO it's not for owners to second-guess official notifications.
Let them send a CC, then perhaps the OP would get the penalty refunded! (I would use ground 2 in any SD).
The OP has until close of play today to make reps in respect of ****1100. (Issued 1 Sept.)