[amazongreenie]

Haven't dealt with that before but have you tried wiggle-moving the seat-back forward and backward while trying to further pivot the release lever(s) so to maybe release the snag (of the teeth of the tight-jammed gear cogs/lateral toothed-rods in the seat's mechanism(s) ?

...some seats have dual seat-back release levers - one down low near the fold and one up near the upper third of the seat's back, in case you didn't know that already