The first time I bought diamonds, there was no proper acknowledgement, the transaction looked like it had failed, and the special was expiring. As is typical, the special only applied outside of normal working hours, so no support responses. I tried again. Both lots of diamonds showed up a day or so later. Net result - twice the diamonds I wanted - and because I'd spent some by the time support woke up, it was unclear whether or not I could get the unwanted purchase refunded. (They seemed not to understand the story I was trying to tell them... I gave up and kept those diamonds.)
Anyway, the point I'm making is - don't expect results till Monday, after the special is over. And don't assume that the transaction failed, and buy more.
Interestingly, my second diamond purchase was for a different account - US rather than Europe - and that transaction took effect almost immediately, with no confusing error messages etc. Perhaps they figured out it was a person they'd already seen purchasing diamonds?