Return of black diamonds

Hello, I have tried to contact support regarding a mistake I made when making my purchase; I will explain my situation now: I would like to request a refund of the 50 black diamonds I spent. When purchasing the speed-ups, I thought they were "free" using the offered coupon, but it turned out they could only be used on specific packs. I had intended to spend those black diamonds on the "Honor Flag" weekly card (20 flags for 7 days), which cost the same amount.

I'm not asking for a real-money refund; I'm just requesting my 50 black diamonds so I can spend them on ANOTHER OFFER in the same game. Since the explanation wasn't very clear, I was going to use it on the other offer. In short, the support team I contacted refuses to give me my black diamonds (50); my purchase was a technical error on my part. I am not asking for a real-money refund. Is there anything I can do to get my 50 black diamonds back? I was going to spend them on a different pack.