Oh that's shitty.. I noticed that too when looking for a friend her flights to here in fall that when I changed the date (in the same session) it would first show me the 15 euro tickets on that day and when changing the date to there it was 20 euro .. and so on.. she also paid double a few weeks ago because she had to wait for permission and saw the prizes rise in those weeks to double prize :( Can't your sister help you out so you can give it back next week? I feel bad for you, those moments are the moments you really want to be there, but due to circumstances you can't.. :( hope you can find a way!