Try sending it back by calling it the wrong part and see what happens. I guess a changed part isn't a wrong one, eh?
I have a little experience in this.
The first I remember was when ordering a new door pull for my passenger door. The original door pull was in bamboo, and I had changed the interior from MB-Tex bamboo color to black leather. The original for a 280SL has chrome plated end caps that are fully symmetrical and cover the mounting hardware. The REPLACEMENT from MB had asymmetrical chrome caps, clearly one was contoured to wrap around a door handle, so it was probably for a sedan.
The second was an official data tag. Let's just say it had issues.
Both were returned without question. I think for anyone who has dealt with the Classic Center knows they are very accommodating and friendly. For the former, instead of new we found a very, very good used one on eBay or something. For the latter, let's just say I went with a reproduction from a clandestine source.
I also did buy the automatic transmission filler tube, and that was painted black instead of cadmium plated. So, we had that stripped and plated. Had we been able to find a good used one it would have needed plating anyway.
Most of the time there is a way out and you just have to be resourceful.