I would also speak with motability and make them aware of whats gone on.
Is the car you orered still on the scheme, if so has the advance payment increased, decreased or remained the same?
If the car’s no longer on the scheme its unlikely you will get it as @Rene says it will get cancelled. If the car’s still on the scheme and the AP has increased the dealer may put it through at this rather than the AP at time of ordering.
ChrisK has made an excellent point, as you will beable to see if Mb are aware of your initial order in your online account.