I have to press brake pedal quite hard

More then likely you have lost the brake assist which is run off of engine vacuum so I suspect you have a leak in the brake booster.

I attached the process from the manual on how to replace this from a similar vehicle. Unfortunately we don't have a manual on this vehicle as it is not offered here in the USA but this vehicle is similar to yours.

Please run through this material and let us know if you have other questions. Thanks