I have used the "time to think" option just once and did pay within the 24 hours by selecting the booking within the Manage my Bookings section. I was then directed to the same payment screen as if I had paid the day before. It worked out seamlessly, but I admittedly had no expectation of getting the EUR 10 back.

With respect to the additional EUR 15, do complain and ask nicely for a refund. I guess that the web incident was too recent for a contingency process to have trickled down to the phone reservation agents. Who knows, you might even get some bonus miles out of the incident.