LG UX 355 and mp3 ringtones

I have a LG UX 355 and I uploaded an mp3 ringtone to my phone via USB cable, I can see it listed but I just can't set it as default. How do I get it to work? Is it a feature that US Cellular has turned off so we have to buy ringtones from them? Thanks for any help!

make sure its a MIDI file
its its an MP3 the phone wont recognize it

I have also tried a MIDI file and it still wouldn't work and the phone is supposed to support mp3 ringtones. I have come to a conclusion that USC has locked it so we have to buy their ringtones from Easyedge which I will never do!