I'd say your liable for damages. Whether it's criminal damage is another matter. I personally don't think it is, you can't get arrested but they might take you to small claims court to get the money if you refused.
Find out your bike is locked up - if you break off the door now you're liable
Make reasonable effort to contact owner and get no response - if you break off the door now you're NOT liable
Get extra information about gaining access - if you break off the door now you're liable
Problem is that last bit where someone came and gave you more information. If you'd just broken the door off quickly THEN someone walked by and told you "hey, I've got a key for that" I'd have been on your side.
Almost identical thing happened to me in my old flat. Factors changed the lock on the car park gate without telling anyone... Queue of people standing around the gate trying to work out the code at 8am before the Factor office was open (so weren't answering the phone). I had about 20 witnesses to me breaking off the lock with a pry bar and damaging the gate and I even emailed the Factor telling them this. They chased me for money to fix, I told them where to stuff it, threatened with small claims court to recoup costs but never went anywhere. I always assumed it was because I was super awesome, but more likely it because I pointed out that they admitted it was their mistake in the email chain.
I'd suggest you try the same. Get them to admit fault (by not issuing keys) and try and make clear that your actions were reasonable. Although, like I say, how you argue that in light of the fact that someone said "hey, wait a minute, I'll get a key" I've no idea.