Q:
Bank Tabs
You can try clearing your GW2 cache (instructions found in the Knowledge Base accessed via the ‘Support’ link above/below).
There are 2 methods to initiate the purchase of Bank Tabs; one through the Gem Store, and one through the Bank UI. You could try both.
If you continue to have issue, you can contact the CS Team via the ‘Support’ link above/below, and ‘Submit a Ticket’ for assistance.
Good luck.