Very slow internet, keeps lagging

I had new service put in about 2 months ago. I have the 1100 mbps plan, but the speeds we are getting are around 75-200 mbps. The connection keeps lagging, especially if more than one person is using it. I have been trying to have someone come out for the past month, but I keep getting stuck with the virtual assistant or an agent from another country that is not helpful. Since it is a new service and winter, we are still waiting for the line to be buried. Animals have been chewing on the line that is lying across our yard and our neighbors. The speeds dropped off significantly after they chewed the line. Yesterday my husband was able to speak with an actual live person in the United States. She was extremely helpful and set us up with an appointment for 3/21. A few hours later, I received a text stating that my appointment was cancelled. 

I have been a Comcast/Xfinity customer since 2001. This is the worst customer service I have ever received. I just want to get in the ballpark of the speeds that I am paying for.