You will have no comeback with this, or any resolution.
There are rules and procedures for joining Motability and if you have broken them, the contract is null and void.
No point in complaining as its obvious you wont get anywhere, just put it down to experience.
There is a lot more going on than passing it off as “we did not know”. Any dealership insists you come in and sign up for the vehicle. There is a few people who have tried to order remotely and could not, they had medical issues and its too much for them.
Motability will try their very best to help their customers. But if you break the rules, then its on you.