Supanet are the absolute worst ISP in the entire world, and that's not a claim I'd make lightly.
Ha! I can categorically state that you're wrong, as I used to work for the worst ISP in the world. (Admittedly, this was in 1999/2000.) At one point we even had 1 (that's one) customer at a time going through a single dialup connection, running through an ancient desktop PC plugged in to the main phone socket of the office.
It's an entertaining story...
http://web.ukonline.co.uk/~eezypeezy/
(I designed that great 'e' logo, by the way, which I was very proud of until someone pointed out that it looked exactly like the Internet Explorer logo.)
The staff said, shortly after I jumped ship...
http://web.ukonline.co.uk/~eezypeezy/comments.html
Ah, my old workplace, a cutting-edge communications establishment...
http://web.ukonline.co.uk/~eezypeezy/ezeboxes.html
Um, this was a long time ago. I bailed out as soon as I could...
He refused to give me a MAC Code "because you're still in contract".
You should really have reported this to Ofcom, the industry regulator, as this is against the Ofcom regulations that all UK ADSL ISPs should be observing. They can still hold you to a contract but they MUST provide a MAC upon request. (Oh, wait, just read that you did this. Good.)