Rear seat is stuck!

Hi I have an Astra 1.7 DTI Hatchback and part of the rear seat has got
stuck. I cannot move the larger rear seat backrest forward or backward.
It isn't locked into position because I can see it isn't locked onto
the catch. There does not seem to be anything causing it to be stuck
however something is making it stick. Help! What's up? The 3-point seat
belt for the the centre rear seat is therefore stuck because it can
only be pulled out of the retractor when the rear seat backrests are
properly locked into position , which it isn't. Any ideas anyone?

 

Oh for the record, it is stuck near to the full upright postion, though
it isn't fully upright and the catch isn't locking. The big button at
the top of the sit is depressed in, just as it is when it hasn't caught
the catch. I

 

Is it not going up because the seat belt is stopping it? If yes can't you
undo the belt?

 

Thanks by the belts (none of them) are done up. Honestly I have checked
and double checked and it is clear that they are not holding fast, the
sit backrest.

It is strange that should a simple thing has become stuck and someone
else out there must have encountered this problem as well?

If so, what's the answer, short of haven't to unscrew all the rear
seats.