Dishonesty over their own terms and conditions

Last year we booked flights to Scotland with travelstart but due to unforeseen circumstances we had to suspend our flights but were told that it wouldn't be a problem and that we could reschedule our flights for another date because we had booked flexi tickets. The only conditions that we were told was that when we rebook that it should be with the same airlines and that the tickets should fall into the same price range or if the tickets were more expensive that we would have to pay for the additional costs. We agreed and when we finally decided on a date and checked on travelstarts website for flights that fit those terms and conditions they responded with DOUBLING the cost of the tickets even though on their website it indicated the price that we had already played. Doubling the price tickets with no apparent explanation and then going against their own terms and conditions doesn't sit well with me.