Trouble with spiral folding bike lock - jammed 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:
Jiggle it, wiggle it, slap it around a little.  The latch part is probably not retracting when it should.   You can also blast the lock with a penetrating lubricant and repeat the jiggle/wiggle/tap.

You could try contacting Rock Bros at http://www.rockbrosbike.com/article-info.php?artid=6   for advice and possible replacement.

Its slightly disconcerting that their email addresses are given as 
rockbrosbike@gmail.com and rockbrosbike@hotmail.com

Is your bike locked up somewhere else?   I'd recommend you go and add more locks to it until this one is removed.  If you give up, use a grinder to cut the lock completely and throw it away.