I've found that baby powder works better than belt dressing. I had this very same problem with my belts and it went on for a couple of months. I was soo sick of it, i swore my belts were tight i reloosened them and retightened them several times.
To get to the point: I asked a master certified technician at my dealership and he was like these are loose, he tightened them so tight i thought they were gonna break(not that tight) but a lot tighter than i thought and they never squeaked again. Get a pry bar or llong bar and go to town, it might be better if you have some help.
Hope this helps you out.