I don't want to but my Grandparents make me! Help?

Ok, so my grandparents are VERY religious and they keep on signing me up for vacation Bible Study, even though i'm too old and they want me to do First communion even though my parents said NO. Who has final say in this? My parents or my Grandparents? Do i get any say in any of this? They guilt me into going to church alot, i love them but i am not a religious person, help?