Rear seat was folded for putting stuff in the back, and now the centre seat belt has ''locked'' so l can not even lift the rear seat back up. After dismantling what l could, l still cannot get enough slack on the belt to release it. Any suggestions?

you have to remove the bottom seat (base)
it might be held on with 10mm nuts. there is a 16mm bolt into the floor holding the seat belt to the floor. just take it out anti clockwise.
you might have trouble getting it out again. l would replace the seatbelt if it was me. app £100.00. if fitting it you must line it up ''TO THE MARK'' hope this helps

l believe the only method to unlock the seat belt is to blow the heap of crap up.