Hi, I have donated 15$ and I got 30 points ok, but after that, i have changed 10 points for 10 diamonds and I don't know if I'm having problems with it, because i don't have them in depot yet. Here some photos to prove I'm not lying:
Normally when you change your points for something, this thing goes directly to your Pokebag, so, maybe you have it full and it doesn't let you receive the diamonds.
If this is the problem, try to clean your bag and then login again.