I might of been lucky but I unjammed mine by dropping the seat forward and locked the seat mechanism with a large screw driver. This may cause the belt to retract so hold onto it. I then worked the belt in and out gently with the seat tipped forward. This freed my belt. You can reset the seat by pushing the release button. You just need to move the belt in and out about an inch. Dont let go of the belt unless you have freed it, as it can retract making it very tight when you lift the seat up.
delboy 54, March 2009