Google Nexus 6 :: Why Cannot Assign Ringtones To Contacts

Like the title says, I am trying to make my Nexus 6 assign certain ringtones to certain contacts on my phone using Zedge. Now I go through the process and it takes the tone and I save it on the contact but then it just goes back to using the default ringtone in the settings menu. I used this to do the assignment and it still won't do it. I don't understand why it won't let me put custom ring tones I contacts, I like to have a ring and text tone for each person on my phone that way I know who it is before I even look at the phone.