My 6 Plus keeps resetting my ringtone whenever I turn it back on

Ok so all I keep finding is loosing purchased ringtones, that's not the problem. I just got my Iphone 6 plus hardly a week ago and any time I turn it off and then back on later my ringtone resets back to default. I still have my purchased ones, but whenever I go to put them back on it claims that's still what I have as my ringtone, but whenever I get a text it's clearly the default tone. What gives?