You should call Motability, they might be able to organise you a courtesy car to tie you over.
On top of that, i’d cancel the order and walk to another dealership. Either another DS, or just get another car. If i get the impression that a dealership doesn’t want “my” business, fck em. Times are tough, and as a motability customer you got choice. Phone around, call dealerships that have cars in your price range and ask what the quickest delivery possible is. Don’t be too afraid to ask for in-stock cars either, most they can do is say no.
At least, that’s what i’d do.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.