Seat Rear Seat Belt Locked

[Euphful]

Seat Leon locked rear seat belt how can it be freed

[TWR]

First, try some WD 40 where the belt goes into the buckle, press the Button a few times and see if it releases, if not, the buckle can be separated with care, if you do manage to get kit open replace the Buckle for safety reasons.

[Baldric]

Or does the OP mean the auto-tensioner has locked-up?

[gingejbee]

Has the rear seat been folded down recently? Locked belts after folding is not unknown on VW-group cars. You need to fold the seat down again and (very gently) pull slowly on the belt....usually moves.

[Old_Jim]

You can normally free it by giving it a sharp jerk, then leaving it to click back into action. If that doesn't work, the mechanism has failed and the belt will need to be replaced.

[Iggle Piggle]

Pull the full length of the belt out then let it retract back into the slot, right up to the buckle, then pull it back to where it's needed.
It will probably make a 'ticking' noise as it retracts, this is a system for convenience fitting child seats in the back and is totally normal, if a little annoying...