Put the complaint in writing to the manager first and ask for a written response. If you're not satisfied, escalate to the agency's principal or director. Still unresolved? Take it to the committee, then to the state regulator (Fair Trading, CAV, etc.) and ultimately the tribunal.
Document everything — dates, names, what was said, what action you wanted. Always escalate in writing so there's a paper trail. Most reputable agencies have a formal complaints process and will investigate genuinely. If they don't, that itself is a sign you should change manager.
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