problems putting ringtones made on garageband on iphone

I can make ringtones on garageband using loops etc then send them to itunes but when I transfer them to the iphone I can only ever have one of them on the phone at any time, every time I put a new one on it duplicates the existing. So if I try to have four different custom ringtones on the phone it just makes them all the same ringtone. Any ideas please.......... thanks