Cannot get help with continual internet performance issue

I have called several times, they have sent someone to my house twice but the problem continues. Calling support is useless, they cannot help and only promise to have someone call who never does. The internet started being flaky several weeks ago. I got a new router and it is activated but the issue continues. I pay for gigabit speed and am getting  about 200mb on a direct Ethernet connection and worse on wireless I work from home and my calls are dropping and dropping out. I need help but no one will get me in touch with advanced network support. Calling in is nothing but frustration and a waste of time. Help!!