This should be one of three problems, either the cable is broken or the release handle is worn and not pulling the cable to release the seat back. Something can be stuck in the track like an ink pen use a flashlight and look down inside.
Here are some diagram (BELOW) to help you get the problem fixed.
Please let us know what happens.
Images (Click to enlarge)
Monday, May 29th, 2017 AT 10:16 PM