if your cable hasn't broken - the seat handle should move and then stick solid half way, if the cable was broken it would be completely loose - then you need to use a large flat blade screwdriver and use the side of the seat hook support bracket as a leverage point. Get under the seat at the rear, jam the blade under the hook but balanced on the side plate, tricky, better if somebody else operates the seat handle, use some leverage and while operating the handle with some force not enough to snap it the seat should just release, try the other side too, one of the sides will free it.
When you have it reclined get some sandpaper out, sand some paint/metal of both the hooks and the bars, it is a simple case of too tight a fit from manufacturer. Grease it all up.