Overcharged on Telus bill. How to lodge a formal complaint?

I’ve been on the phone with Telus for over 6 hours getting transferred around in the last few days and no one seems to know what to do. I was told by an agent that the charges would be removed from the bill, and called back today as they showed up on the new bill WITH a $75 late fee. I was told “Sorry, that wasn’t valid. They shouldn’t have said that. You owe us $365 now”. I asked them to listen to the recording from the last conversation and they refused. Now I’m on the hook for almost $400 because of their mistake. How do I lodge a formal complaint against the customer service rep(s) and who do I contact outside of escalation to get this resolved?