Maybe you should first get written proof that MBNA has credited Diamond Club, and with this info, then send it to the DC centre to say .. well, here it is.
No use calling really.. cos they have to see it that the former has sent the info in.
I had a 1000 miles credit from Hilton Honors. Hilton Honors said that they have sent it. DC said they haven't gotten it. So I got my invoice and faxed it to DC.
Well, I am still waiting but at least there is proof of my stay.