Sounds like an IT glitch, which will doubtless be sorted in a few days. In a sense you shouldn't need to be too concerned, if you have passed your payment details on to BA - the whole set up is entirely contractural in scope and so you should feel you have a confirmed ticket. I can see they may redo the transaction after the 72 hour period but will do so based on the original terms, not on current pricing. Obviously take screen shots and notes of who you spoke to and when.