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If the vehicle has been in a wreck and the seat belts will not unlock you will need to replace both the seatbelt and buckle to fix the issue. Their is not a lock release on the belts and if you were in an impact large enough the belt mechanism is damaged allowing the lock mechanism to not release. Also the buckle has a cable in it with a load that if the vehicle sees an impact will make the belt lock in and pull very tight to prevent you from moving around in an impact when the airbags deploy. The only thing you can try to save the belt assembly is to cut the belt buckle to open up the area to free the belt. The buckle assembly has to be replaced anyways so cutting it is no big deal. Also keep in mind if the buckle is locked to the point where the seatbelt cannot be released it is a very good possibility that the metal part of the belt at the buckle may have some form of damage to also need to be replaced depending on the severity of the impact. If you have any questions please let me know! Thanks once again for choosing Just Answer!