What nonsense.
And you wonder why Motability customers get treated as second best.
A deposit shows the dealer that you are serious about ordering the car.
We’ve had two on the scheme and both times we’ve put down a deposit of £500. We did add options.
No way would we have been able to order an Audi or a Volvo without a deposit.
Having said that, it’s correct that the deposit forms a contract between the dealer and the Motability customer. So people don’t change their minds.
I hope the OP gets it back but the dealer has no obligation to do so.