Sorry for what you experienced my dear Cupart.
I can share my very recent experience with the "time to think" possibility. I used this feature for the 1st time last week. First, I'd like to clarify that the 10€ fee you pay for this option is clearly not deducted from your fare when you confirm your booking. It's a fee you pay to have "the time to think" while you guarantee your airfare during a week (as fares can increase rapidly with time as more bookings are done for your flight). In my case, I confirmed 3 or 4 days after booking, so well in the allowed time window. I accessed my booking from the web page "manage your reservation" and paid as if it was a regular booking. But I had a problem during the payment process : after giving my CC details, the page where you have a red butterfly and asking you to wait while they are processing your payment lasted forever (in fact, I had to stop it after 30 min). I checked my booking after and obviously my booking was not confirmed but I did not want to do it again on the web just in case to avoid double charge. Then, the following day, I called the internet help desk number and explained the situation. They were very nice with me and they finished the process. But they did not charge me an extra 15€ as for you (but I will immediately check my bank account to be sure ).
So Cupart, you are definitely entitled to get refunded for the extra 15€ you have been charged.
Let us know the outcome of your discussions with AF.