"Please" leave us without a penalty..
It definitely sounds like an OpenReach issue - so you can see why ZEN want this guy to leave ASAP. Any future ISP will have the same issue, so he'd be far better staying with ZEN and insisting that based on the contract that he's been paying, THEY need to get it sorted.
I've had problems with BT recently (not naming the product), and after months of zero support, I started "abusing" every one of their adverts on Facebook - all done very politely by just pointing out how bad they were. Within a month of my campaign, I'd got a call from someone high up who asked "if I'd had problems?" :-) He's not put me in direct touch with someone technical who actually understands the product - almost a happy ending - it's still not working correctly, but they guy I'm talking too actually understands the problem and appears to be kicking arse and getting some progress.
This article, and a lot of public exposure of the issue will do more good than writing to your MP - in fact, despite my local MP having broadband and a website, he doesn't "do" email? :-( (he does do email, but only for his friends - not for his constituents!).