Collection Expander Bug
When you buy it, the game send you a mail with a token. Accept the token to your inventory, and then double-click on the token. That will unlock the ability for your collections to hold 500 instead of 250.
Also, remember mail queues. If you have 10/10 or even close to 10/10 mail saved, your purchases from the Gem Store will sit in the queue until you delete several mails. Good luck.