Slow internet speed and connection dropping since summer

Hello,

I have been having trouble with my internet connection since this summer.  Speeds have been slow, and there have been varying degrees of connection problems.

On 12/2 I had a chat agent activate a new modem, but the same problems persisted.  The chat agent set up an appointment for a tech to come out, but after waiting for the appointment I contacted Xfinity only to find out my appointment was cancelled without notification.  During the week since the new modem was activated, the connection problems have become worse, dropping every couple minutes.

I have been forced to use an old 4x4 modem in the meantime, which maintains a solid connection, but isn't capable of providing the speed of my plan.  I am using an ethernet connection to the modem, and the coax cable is one cable coming from the outside line - there are no panels, jacks or splitters involved.

Any help you can provide would be appreciated.