No birth control refills

I'm supposed to get my birth control prescription refilled but my doctor keeps on denying my prescription. I'm supposed to get one last pack because they didn't notify me on the deny but I still haven't gotten my prescription refilled because they "forgot" to send it to the pharmacy. I have a appointment next month to talk about my prescription but if I haven't gotten my refill yet I don't think I'm ever going to get it. It's a Catholic practice doctors office so they probably aren't going to give me my prescription anyway if they know I'm sexually active ( I originally went on it because of medical reasons). I've had problems with them before on this subject and I'm really considering just calling it quits and going to planned parenthood for my pills instead. My mom wants me to just stick it out and go to the appointment anyway (I'm 18 by the way) because we made such a fuss over the prescription but I don't want to! They aren't very willing to work with us on this and they aren't very nice about it either. What should I do!? What do I tell my mom?