Your Owners Corporation is right!
The electrical switch room and everything in it (e.g. meters/fuses/switches) is Common Property, so all necessary repairs therein are entirely the responsibility of the Owners Corporation, and there's no need for Owners or their Electrical Tradespeople to have access.
There are limited circumstances when an electrician, having assessed fault/s within a Unit and its electrical sub-board (all Owners' responsibility), wants to check the Unit's main supply in the Meter Room. In these circumstances, I've never found an electrician who didn't have the Master Key issued by the local Supply Authority.