Does the packing slip say Mini? Or does it say
Mavic 3?
I concur with everyone else. You ordered a drone, paid for it, and received a drone. You informed them of a mistake, but you have now been out the $1400 for 4 months, unable to use the money. They are putting you out by not returning it. I am not a lawyer, but I think if you have a decent communication history logged, I think the law would be on your side after 120 days. What if you ordered the drone because you had an event or job you needed it for? Now your out the drone and the money until they decide to respond? It needs to be reasonable.
I know if it were mine, I'd be opening it around the 3 month mark and using it. Especially since if push came to shove, I'd rather have a
Mavic 3, and worst case is they come back and demand you pay for the
M3. I'd force them to make a concession on the price, say $500 off on it since it was their mistake and it was no longer a reasonable amount of time. But like I said, I think the law would make any lawsuit against you very hard and costly, and it would be easier to give a discount and let you keep it.
Since DJI can't force a retailer to sell for a certain price, and you paid them money, I don't think DJI would deactivate it. It wasn't stolen, there was no retail fraud here. DJI can set minimum advertised pricing, but they can't actually set the price, otherwise that is price fixing and illegal. If company wants to lose money, DJI can't stop them legally.