Probably should make sure that we’re even talking AP here, since you call it deposit. Dealers can and do ask for deposits all the time. If the dealer asks for a deposit, it could be that he intends to make sure you pick the car up after the new prices drop, rather than cancelling and ordering a shinier car from a different manufacturer.
AP is not a deposit, dealers don’t call it deposit either. A deposit is always (by definition) part of a bigger payment. You never clarified if you called it a deposit, or they did. In fact, Motability on the webpage even states that AP is not a deposit, in the first sentence of “What’s AP”.
Further, i’d also call them and explain the situation, rather than acting like this. They seem nice enough, not quite sure why “we’re having a laugh” here. Maybe i’m too old for this stuff, but my first instinct/course of action would be a call to them, explain them what’s going on and why you’re not paying right now.
That’s just me though.
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.