Why would my parents lie to me?

I was suppose to go to Paris to study this year and they didn't want me to so I made an agreement to defer my enrollment a semester and study here in return that I get an extra long summer vacation in Europe. We go every year so I wanted this time to be a bit more special and longer. Now they blatantly have ignored our agreement and are cutting my vacation shorter than planed. Why would my own parents cheat me like this? Now it is too late to go to Paris for college this year and I'm left screwed over. This was not the plan at all. I'm deeply offended. It is not a money issue at all. I stay with my grandmother in Europe so there is hardly any expensive difference concerning the length of stay.