Poor Cable Modem Connection

As of this Monday, I've been experiencing wildly erratic connection speeds from 98mps to 1.8Gbps. When I log into my cable modem, it states that the connection is poor, specifically the downstream and upstream status. I've been trying to explain this to customer service, but they wanted to send someone out to check it. This seems like a problem with connectivity outside my home, not inside. How can I get someone to test this and confirm my theory?