I've checked you had the right VRM and bay location code* so this should be easy. Just send:
Dear Enfield, the contravention did not occur as I had bought parking rights at the time of the alleged contravention.
Please find attached the PayByPhone receipt.
I look forward to early confirmation of cancellation.
*The code in the CEO pic is correct but I can see an inconsistency - your receipt says Enfield Highway but I think you were in Brick Lane as per the PCN?