Please explain where each sign was in a better way. The sign for October has no street view so one cannot actually see where it was located. So please tell us exactly where each sign was using GSV and a detailed description.
Sorry if I seem thick , but it's important to know the spatial relationship of each sign.
The council have completely boobed, (stupid and dozy Havering !!), because keeping up the old sign is very bad practice and misleading as you found out, so once we can work out where the two signs were, we can probably help you write a robust representation against the PCN.
Just be aware that Havering will not re-offer the discount if you submit reps. Of course they haven't considered that this will make additional work for themselves, because it is then a total no brainer to take them to London Tribunals if they reject them. They then have to prepare an evidence pack and pay the adjudication fee. Complete idiots, basically