The governing body for strata managers is Strata Community Australia. Go to https://nsw.stratacommunity.org.au/ to find their contact details. They may mediate in a disute with your SM. If your strata manager isn’t a member of SCA, that’s another matter of concern for you and you need to look at their contract very closely to see what your options are.
Meanwhile, you need to gather evidence of what they’re doing and not doing that is contrary to the terms of their contract. But bear in mind that this is mainly a contractual issue and there are very few tasks that SMs are legally obliged to undertake without a direct instruction from the Owners Corp.