do you mean the committee should pay for the work or the owners corporation?
The committee is essentially the Owners Corporation and can make some decisions on the OC’s behalf. You should probably accept that you aren’t going to get this resolved at no cost. When you buy into a strata scheme you inherit a lot of the responsibilities and commitments left by the previous owners. It’s up to purchasers to do their best to make sure everything is clear and unencumbered.
There are theoretically ways you can make the people responsible for a fault pay for remediation, but they often aren’t worth the time, energy or financial cost of pursuing them. For instance, you might be able to make the vendor pay for the unauthorised renovations, but it would cost you more in legal fees and hassles to do so.
Nothing is simple or clear cut in strata disputes.
I strongly recommend that you go to the Fair Trading Living In Strata web pages and have a thorough read of what your rights and responsibilities are, as well as how complaints are handled.