Welcome. No one pays Excel or the other scammers. Do you still have the "little square note" that was under the windscreen wiper? It is a scam but a legitimate one, for now.
I would forget about appealing it with either Excel or the IAS. You may be past the appeals process stage anyway.
If you can, it would help if we can see a picture of the "little square note" and also the Notice to Keeper (NtK) that was sent a few days later. You will need to redact your personal info and any PCN number and the VRM. Leave everything else visible, especially all the dates and times.
The Parking Charge Notice (PCN) has been wrongly issued and therefore Excel cannot relay on the provisions of The Protection of Freedoms Act 2012 (PoFA) to hold the keeper liable. They have no idea who the driver is, unless the keeper tells them, inadvertently or otherwise.
As the appeals process time is likely passed, you are going to receive reminders and eventually Debt Recovery Agent (DRA) letters with the amount increased to £160-£170. You can safely ignore all those reminders and DRA letters. Never, ever, communicate with a DRA. They are only employed on a no-win, no-fee basis to try and scare you into paying up. They are in fact powerless to do anything. Just use their letters as kindling or line a cat litter tray with them.
We will put together a complaint for you to send to Excel, for what it's worth, to see if they will cancel but don't hold your breath.
This will only be over after they have issued a county court claim which is very easy to defend and is 99% likely to be struck out, discontinued or won, some time early next year. You really shouldn't have to worry about this and we will assist you all the way. We do this many times a day.
Please read this thread for instruction on how to post images:
READ THIS FIRST - Private Parking Charges Forum guide