how can I get my bike lock open again?

[woodencoffeetable]

it's one of those heavy chain ones (decathlon), that have a hook&loop (no idea what the technical term is) mechanism.
the key turns and I feel the slight resistance but the hook doesn't open.
sprayed generously with caramba...without luck so far.
what else can I do?
my google skills fail me and I only get videos of bike thieves.

Bolt croppers for the chain?

luckily the lock is not locking the bike currently.
t'was an expensive lock, if possible I'd rather not have to get a new one...

I'm not familiar with the product you used but how about spraying liquid graphite or silicone spray into the lock mechanism...or maybe take it to a bike shop or lock shop...they have all kinds of tricks...I wonder why it jammed in the first place. You said it was expensive, but if it is going to give you problems it may be time to get a new one since you wouldn't want to use it on the bike only to have it jam again.
Ok, this may sound utterly stupid, but are sure it's the right key? I ONLY mentioned this as I've tried to open locks before and accidentally was using the wrong key that looked similar...a wrong key will fit in the mechanism but just won't turn the pins or tumblers. Good luck!