Technician just closes fault without resolving it

My line has been unstable since activated and I am trying to get someone to resolve it. Frank came out on Sunday, and said it might be my router, or I might have to reduce the line speed due to distance from the exchange. He promised to return later on Sunday or Monday with a router to test, and if it then turned out not to be the router, he would try the line speed. He left and never came back to me. Instead, he closed the fault and I received an automated SMS that I couldn't reply to telling me it had been resolved (which it has not). I called the call centre today, and they won't reopen the fault, and are unwilling to assign another technician to pick up where Frank abandoned the issue. Now I don't know how to proceed, and am exceptionally angry that the Fault Reference was closed without attending to it.