If it’s another completely separate strata scheme, I can’t see where mediation would come in. It’s certainly not a strata issue.
Your council should have some means of making a noise complaint. It sounds like they are not in breach of their DA but are in breach of the EPA. So pursue that and think about seeking a noise abatement order at your local court.
Noise abatement orders are explained in the links posted previously.
Your strata committee should be a bit more supportive on this but you can do it without them if need be.