Spotty Internet wi-fi and streaming

Been having the same problem for over a year. Wifi is intermittent, streaming intermittent. Replaced router, had technician come out and check everything inside. Had a Technician come out and check everything outside. (Charged $100 for visit). He informed us that the problem was not with my equipment, the problem is with the mail line. No idea when, how or who is planning to fix the problem. No Idea who to complain to. I call customer service and begin the same, reset the router and try this and that, but when I call, everything seems to be working, til it's not. Can I speak to/email an area supervisor to find out if there is any plan to fix/improve the service.