Mobile Data not working on Samsung Galaxy SIII

I found a few other threads with similar problems, but none of them were very recent, and they seemed to have slightly different circumstances, so I thought it best to start a new thread. 

My GS3 won't connect to anything that requires mobile data. It all works if I'm at home and connected to WiFi, but when I leave the house nothing works. I checked my APN settings and they seemed to be OK. I even tried adding a couple of other APN's that looked like they might work, but that didn't help either. I've power-cycled the phone numerous times and that hasn't helped.

Last month I had some financial problems and I had my service suspended. I first noticed this problem after my service was reinstated a few weeks ago.

My phone is currently running 4.1.1, but I just started the download for 4.1.2.