Not just Openretch
I've had the same problems with France Telecom. We had a flaky line that was erratic in hot weather, it took 5 calls and 3 visits before they finally sent out a competent engineering team instead of a pole monkey. They found and fixed the fault (an intermittently flaky connector).
As noted above, people want cheap internet, so frontline help desks are staffed with script-reading "have you tried switching it off and on again" types. Once you get past them things start to move.