Slow internet - throttling suspected - cannot talk to a live agent

We pay a significant amount of money every month for 600Mbps. My wife, who works from home, is not even reaching 20Mbps and often has her video meetings disrupted by the service. She is a professional and having meetings drop often is not acceptable. I do not need help troubleshooting or placing the router in the best location. I suspect she is being throttled as other devices on the same network and in the same physical location are not having the same bandwidth issues.

The automated messages are completely unhelpful and are a waste of my time. I am unable to speak to a live agent and call back is always mysteriously unavailable.

This is the worst customer service I have ever experienced - even worse than AT&T which is looking like the direction we will be heading shortly.

Any advice?