So I had this happen to me. One upon a time many thousand years ago, I had rescheduled but not paid for my tickets on the phone. I was asked to make the payment in the next few days (at their offices I think). When I went to make the payment I was told that the prices had increased. And by quite a bit.

I marched down to AI House and spoke to one of the leaders (possibly the station head). I don't remember his designation but his office room was almost as big as my house! I explained my situation to him and argued about it for a few minutes. After that he told me to give him some time and come back in an hour. When I returned he told me they would honour the original price they had quoted to me.

Now the situation might have been different then and you might not be able to engage with a senior enough person to get this fixed for you. I'm not sure what this guy did - whether it was some kind of waiver or fixed an error that AI made when they told me prices had increased, but doing this is certainly possible.