If the strata council still refuses to add the resolution to the AGM agenda, what can I do?

Firstly, section 43(6) does not apply. So, the owners cannot give notice and hold their own meeting to vote on the resolution. To do this, the owners must give notice in terms of section 43(1).
Secondly, the strata council will be in breach of the Strata Property Act. You can use any of the available dispute resolution methods, i.e. sue the strata corporation in terms of section 163, make application to remedy an unfair act in terms of section 164, ask the court to instruct the strata corporation to perform its duties and stop contravening the Act and the Bylaws, give notice of arbitration in terms of section 177, or commence action through the Civil Litigation Tribunal.