Thanks for the advice!

I'm actually around 100k short now so leaving it as is would be the better deals vs. claiming a refund of the fees they overcharged me. Nevertheless, I decided to come clean and contacted them via chat.

Unfortunately, their response was inadequate so far. No acknowledgement of their IT chaos, instead they said it was normal for their system to charge new prices a day before as tickets would only be issued on June 15. I did receive all of my Electronic Ticket Receipts on June 14 though, so that makes no sense to me.

They said they would check with back office now and get back to me within 24h... let's see how that goes...