28 April is the relevant date, so you booked this before then and therefore should have got the higher rates.

You will see the thread linked in by nux. What you should do is raise a general webform, include PNR and ticket number, wait until you get an automated response with an incident number. Then a day or so later you can fax in the itinerary from IB showing the date you booked the ticket. Make sure the incident number is on the fax. Pro-actively sending in the itinerary may save you a bit of time. Mention in the webform that you will be faxing in the itinerary. The fax number will appear in the Contacts section at the bottom of your BAEC main page.