"It took about three hours and I still the guy is a legend."
What you had there was an "old school" engineer who actually understands how telephones work, rather than an "appeasement" engineer who just plugs in a JDSU (the little machine that goes "ping!"), can't find a fault and reports the line as "right when tested".
This happened to me three years ago, when my line got dumped into a "hot" VLAN after an exchange upgrade, and peak speed/latency went down the toilet in the evenings. BT sent out multiple SFI engineers, including some poor sods who didn't even know WHY they had been sent out ("Have you got a problem with your line, mate ?")
Fortunately, I'm with AAISP, and they gave BT a jolly good kicking (as is usual for them). They took it up to High Level Escalation and eventually got it fixed.
Yes, they're bloody expensive, but if something breaks, it gets fixed. Or BT/TT get another kicking.