iTunes match doesn’t seem to be working on iOS6 for a lot of people.
Every device of mine was fine until iOS6 and the iPhone5. When I went to play a song, the phone waited for a second or so, and then went crazy. It skipped to the next song and the next song and the one after that. Looking at it in the iTunes app, it was attempting to download each song for ¼ of a second and then going on to the next.
Even if I turned my phone to another app and had the music on pause, it would skim through until it found one in my downloads. We often got to #538.
I went to the apple site and got the usual unhelpful gubbins.
I tried the turning it off and on, disabling network data, resetting music device, resetting settings, resetting phone, but it wasn’t coming back.
Finally, I was on iTunes proper on my mac buying a song when it appeared that iTunes Ts&Cs had changed, meaning that I couldn’t buy.
Once I had updated my Ts&Cs iTunes Match was back on my iPhone. Problem solved.
It strikes me as pretty poor that Apple doesn’t give a correct error screen when on the music app or the iTunes app when using iTunes Match. It’s up to you to work out the problem yourselves.