How do I release a bit from a jammed keyless drill chuck?
I recently had the same issue and tried numerous solutions with no luck. In the end I purchased a strap wrench: This kind of wrench grips the object via a strap or a chain:

You basically put the strap around the chuck, tighten the strap and then use the wrench handle as a lever to gain more torque while trying to undo chuck. This worked extremely well.
I simply wouldn't bother with any other solution in the future.