Music keeps deleting itself

i have been issues for a while trying to keep the music that I've downloaded off my cloud from iTunes Match on my phone. For some reason the music that i have downloaded for offline use, does not stay offline or doesn't seem to be actually stored on my device. I have built a playlist to keep myself from going to each song itself to download but that doesn't seem to help because I have to constantly download the playlist. In any case, if anyone has have been having this problem and know of a fix, I'd be glad to hear it.

P.S : I only use the cloud / iTunes Match to put songs on my iPhone