I question why the dealer thinks you will loose £500 if you cancel. Your contract is with Motability and only signed electronically when you enter the PIN. The paperwork you signed at the dealers is a retail invoice and only serves the purpose of ordering x on behalf of Motability.
The fact your dealer wouldn’t be prepared to lower the AP, if it went down between now and collection, ontop of wanting £500 would have been enough for me to walk away and orderd elsewhere.
Skoda (VW) dealers act as a direct sales agency for its EV’s in UK and will do the same in the rest of Europe. Meaning dealers profits on selling EV’s will be lower than ICE, which continue to be sold as before. Understandably dealers are issed of, as profits will come from servicing etc – hence they will try anything lol.