If it’s a Motability car then the hoist is ordered from the same dealer/salesperson your getting the car from. What the dealer has said about sorting with Motability is wrong as its them, the dealer, that should sort it. Not sure where you stand if you never ordered the hoist the same day you ordered the car but I think its still down to the dealer if the car has not been delivered and they can’t fit the hoist until the car is at the dealers anyway.
The dealer should be in contact with Motability recognised adaption installers who should sort thing like steering balls or what ever other adaption you may need.
I don’t know what it is but some dealers seem as if they can’t be bothered with anything else but the car as if adding the adaptions and hoist is someone else problem. I think it maybe it’s because there in an area where they know little but generally more experienced sales person know the installers of the adaption as they have their favourites.