You didn't specify the payment method, so I can only speculate.
If it was a first-time PayPal purchase (no matter how much you may have spent on the game previously), then it can take up to 24-48 hours--depending on when the purchase was made--for your diamonds to arrive. Considering that you made the purchase on a weekend
and today is President's Day, a Federal and bank holiday, it may take longer for a new PayPal purchase to clear. This is a PayPal security feature, not one instituted by Gameforge.
It may make a difference that you're putting diamonds on a different server this time around, but I don't know that for being a fact. Again, speculation on my part.
Diamond purchases are automated, so they're untouched by human hands. (An image occurs to me of a boiler room full of Chimpanzees, but...never mind.

)
If you haven't received your diamonds, you may wish to consider contacting Support. You can use one of the links on the site's main page or the Contact Support link in my signature. If you haven't already created a Support account, you will have to do so when you get to the Support Portal.
In your ticket, provide as many details as possible: When the diamonds were purchased, diamond package bought, payment method used, game account name, server the diamonds were going to, and so on.
Above all, please be polite. You're corresponding with a person, not a machine. Even though you're upset--and I do understand that--being irate in your ticket will not help matters at all.
While there's nothing I can do directly to help you, I do apologize for the inconvenience.