Frazzled & frustrated at Voip quality

First ime posting. Hoping you guys can help. First, when it works, it works well, when it doesn't, my 'gizmo' as SR calls it, is no better than a paperweight. During the time I need it most, the business hours is when service is worst. I can hear them, but they can't hear me. Comcast cable says it's a problem with Sunrocket and Sunrocket says it's Comcast. Can someone tell me who is the problem; where the problem lies, and how it can be fixed? I've power cycled the modem, still no change. I unhooked the router and connected the gizmo accordingly, still no change. I'm ready to cancel my service and go back to a landline. DL: 13.9; UL: 368kbps; Quality of Service: 63%; Jitter 44%; MOS Score 3.7. Thanks, CHuck