Hi Frank,
That seems fairly negligent on the managing agent... they should have advised you that in the case of an emergency access can be granted, this would be deemed an emergency as it was causing significant damage to your unit and by the sounds of it further increased the damage as it has been going on for sometime now....
I would get into the apartment ASAP (if your agent has after hours support I would say to get them to arrange a plumber and locksmith in order to gain access and then change the locks)
The further this goes on the more likely there will be more damage caused!
They, in the morning call the agents and advise them of the damage caused to your apartment, state they were negligent by not fully advising you, process your claim through the block insurance and seek to recover the excess via the agent!
Ultimately if its not sorted soon, the number of apartments affected will rise, in turn affecting the claims history and the premium paid for the insurance... all these things add up!