I've had the same problem with Adorama. TWICE!
Because they close at 1:15 eastern on Fridays, they would answer and either hang up or transfer me immediately.
Not only was the bag the wrong size (6MDH vs. 7MDH) - but it was the wrong color. They sent the black and oatmeal-colored 6MDH TWICE, not the black and blue/gray 7MDH one.
Accoring to Monique, the CS rep (very helpful), The only way to go about it is to have the warehouse physically check it with a CS rep and a salesperson while having them look at the screen. I will be doing this on Monday.
If they don't get it right, or at least treat me with courtesy, this will be my last attempt with Adorama. They simply ignored WHY I wanted a refund and sent another one. I'm really disappointed. I shouldn't have strayed from B&H.