Ahh I guess that's where things go wrong. I can't say how it works in Europe or whether that's common or not since I'm in NA and know more about how it works in North America but are you able to shop around to other banks for mortgages that do allow early payments against the principal? Is this early payment thing even common?

At the end of the day the bank still needs to make their money but you still need to get the best deal you possibly can so don't get pressured into taking a loan if you have time on your side.