The dealer must be smirking up their sleeves at the nice profit they could make on the A5 for the sake of an afternoon's valeting. Maybe a tad long in the tooth for their own forecourt but the main dealers have secondary channels to clear older trade-ins. And of course they have lost nothing on the A7 even if they give you a few quid in compensation - there would have been a few thousand added in as profit.
Time to get a full refund on the A7, get the A5 back and sell it privately - or trade it in for a car you DO want. (Or maybe even keep it and use the free service)