Did you check to see that the beater brush, the brush that the belt drives, is free of debris and moves freely? When they bind up they can cause the belt to break. Remove the beater brush just as you do when changing the belt and clean as best you can. There are retainer clips at each end of the brush, add some WD40 between the clips and the beater brush and turn by hand to free it up. Reassemble making sure the belt is on in the proper manner so that the brush will turn in the correct direction. If you find this solution helpful, I would appreciate a Thumbs Up from you!
Thank you. Paul