My washer started smoking and smelling like burnt rubber when running a load and when I removed the front panel, the drive belt had burned through.

I replaced the belt and ran a test load and it looked like it was going well (water started to pump out during the final spin cycle) but then it started making a screeching type of sound. I looked down and the pulley on the motor was spinning but the new belt was not grabbing the pulley. The new

belt seems to be in fine shape still (i.e. it's not burned) I replaced the idler spring thinking that this might put enough tension on the belt to get it to stop slipping but that didn't fix the issue. I don't know what to do now. What should I check next?