Common Property Replacement made by Property Manager !!

Herewith my latest issue for comment and advice by my fellow posters.

I have a situation where a Property Manager has, without advising the Owners Corporation, replaced a thru-the-wall exhaust fan in the Common Property wall of the Bathroom in a Unit that they manage, and simply sent the Contractor's 4 month-old Invoice to the O/C for payment!

That the fan is actually a “Lot Owners' Fixture” on our Plan, that the cost of its replacement was over $600, and that the installation is of a very, very poor standard is not entirely relevant to my issue, but all are complications!

On receipt of the Invoice I immediately returned it to the Property Managers together with a note stating that, as Secretary, I'm not prepared to pay it because the O/C:

1) was not advised before the replacement of the fan undertaken

2) was not given an opportunity to inspect the fan and to make an assessment of what needed to be done, by whom, and by when within any constraints that may apply (e.g. budgetary)

3) because the Contractor's Invoice was made out to a third-party (the Property Manager) and not the O/C. 

The complications are not entirely relevant, the fan is “Lot Owners' Fixture” and therefore the Owner's responsibility unless we could have determined that it's failure was due to an insured “event” – which we couldn't have, but it wasn't.

My concerns are to ensure that my rationale for not making the payment is sound, and equally to find a way to have the work properly re-done in circumstances where the O/C didn't engage the Contractor involved (and never has), where the O/C shouldn't have to pay for that additional work, and where the Unit Owner has I know not been advised about any of this by the Property Managers.

Any advice will be as always gratefully received.