Nope, wasn't me I'm pleased to say, for alas I can only assume your joy is a double-edged sword ?
As always, my caveat is, I wasn't on-site and so do not know the full-story by any means, and can only comment on the OP's posting.
To begin with, if you had "50v of battery" on your line, that shouldn't be there, the chances are you wouldn't have had any DSL signal at all. Most 50v contact faults are found in the Exchange (where scrap wire can bridge neighbouring pairs), or trapped in a DP lid, etc ....... it's very, very rare to have a 50v contact in a faulty length of cable ??
Talking of which, I can only assume the engineer didn't locate the actual fault within the 200mtrs of cable, which should have been relatively easy with that ammount of fault voltage on it (Using the Wheatstone Bridge method)?? I can also only assume, that he hasn't found any spare pairs within the cable to swop your circuit onto, as you also say all he's done is reverse the wires in the Cabinet ??
Again, if this was a 50v contact fault, it wouldn't do much good. Certainly, a few 'fault volts' can be 'soaked up' by ensuring the faulty leg is connected to the 50v feed leg, as opposed to the Earth leg, which can fool the DLM but it's still a fault voltage at the end of the day. When the test systems are applied, they feed voltage is disconnected at the Exchange and subsequent tests are against a 'dead pair', the fault voltage will be detected in this way.
Something doesn't add up at all, and I think there's probably more to the resolution of this than you may have been told, Ixel. However, it does indeed sound like you had somebody prepared to try, and a result of sorts has been accomplished.
I sound like a right old misery guts, chucking water on your fire, but I have to say it as I see it (circa: Roy Walker).