Just to update - finally got everything ironed out, but took over six weeks of pestering to do so.
The connection I had with Zen was faultless, but the customer service I received when leaving was pretty much the worst I've experienced... and I've been dealing with BT recently.
I would probably still be trying to sort out a refund if I hadn't been chasing them up constantly. Trying to get them to realise anything other than what is currently showing on their system, even if it was common sense or blatantly obvious, seemed impossible.
The illusion of paying a premium and thinking you will get a premium service is an illusion I won't be falling for again.
Pipex > Zen > Be > iDNet > Freeola > Zen > BT Infinity 1