Whale said:
… it may well have been on the basis that it would arrange and pay for the works and then recoup the costs of that and the ongoing maintenance services from the individual Lot Owners.
Just to be a bit nit-picky, if the OC pays for the same service for all owners, then the cost has already been covered in their levies – no need to send them bills. The only reason to do so would be to transfer ownership to individuals which seems unnecessary since they can be charged for any common property that the owners have damaged (as appears to be what they are trying to do here).
The contractor should be paying for the damage – not the lot owner or the Owners Corp.