The tapes are being 'chewed' because the Take Up Spool is not taking up (Spooling) the slack tape.
You have the following options.
# Open the cover of the VCR (2 side screws and 2 screws at the back), and observe what is happening. In all likelihood the Take Up spool (Right side of the cassette) is Not spinning. IN this case, observe why?
# Shut the VCR, unplug the machine, and open the bottom cover. Is the Drive belt fine? If it is broken, cracked, etc, it will not be able to spin the Take Up spool. Replace the Belts.