No internet or slow line speeds

Since i upgraded my line from 25/25 to 200/200 i have been getting issue after issues. No internet at times and the line speeds are pathetic yet i have to pay my monthly bill for a 200mbps line. I will not be paying the bill as i am not getting the speeds nor do i have a stable internet as was promised. Further more they swopped the router and cables and keep blaming me for cable issues and wrong router settings and so forth. They have to be the worst ever ISP i have dealt with