I use a spiral folding bike lock similiar to the one here: http://www.amazon.co.uk/RockBros-Theft-Folding-Hamburg-Colors/dp/B00MB7NUB6
It was a fairly decent lock, but now it's jammed; I've tried all of my spare keys and everything and the lock just refuses to budge.
Here's what happens when I insert the key and twist it: I am able to twist it fully as if I would open it, but then when I pull the key out, the locking mechanism refuses to pop out; it sort of just stays there when in fact it should release the lock.
I have no clue what to do to open it. I'm not sure if a hacksaw would work as this thing looks strong enough to take one and I have no clue how to fix the jam.
Here's a picture of the bike lock: