contact ringtones

me me me..
someone please HELP

here is what i do basically. I connect my phone to the pc, load an mp3 into the phone, go to my contact list, and select that specific mp3 for one user's ringtone. When that person calls, i just get the normal ringtone i use for everyone else.
I then tried loading into the phone as a .wav file and same problem.

I then decided "well, maybe it's the file i'm loading" so just instead changed that user's ringtone to a different one that came with the phone initially. Tested it out and STILL get the default ringtone that i use for everyone else...

help?????????? i'm running out of ideas and the manual doesn't help at all..

just to add, i also turned the phone on and off and it still has the same problem......no custom ringtone even though it's clearly set and saved into the contact

the only way ive found to correct this fault is to do a master reset.......but you will lose certain things unless you copy them to the media files......also ive been making backups through the software that comes with the phone so i can restore if it happens......to be honest though it is happening everyday with my phone even though it has already been back for repair and has had a software upgrade.......it is a right pain......its gonna be going back again tomorrow to see if it can be sorted....no idea if it is a software problem or a phone problem???????????