Penalised for buying Forex due to a bad system

I purchased Forex last night for my trip to the US and UK in April. I used FNB's online banking and the Travel section within Forex. The process was simple, I inputted my personal details and the amount of Forex I wanted and the system let me purchase this, taking the money from my account instantly. There were no messages / warnings / errors on the site. The next morning, I received a phone call from FNB informing me that I had purchased Forex too early and that you can only buy Forex 60 days before travel, while my trip is 68 days away. They then informed me that they would refund me, but at a LOWER price. They gave me the money I'd paid less R550.21! When I argued with the lady, she told me that this information was in 'Terms and Conditions', which is a tiny link on the page. This 60 day rule is a PRE-CONDITION that should be validated when the user tries to purchase - the system should have PREVENTED me from buying this in the first place! Or, there should have been a warning on the page at the very least. This should not be hidden behind the terms and conditions link. This error was made due to poor usability of the system. I am asking for FNB to please give me a full refund