The policy of discretionary refunds is one that NTL apply very fairly, in my experience, although treating whoever one speak to at NTL on the phone like a human being, ups the chances of discretion being considered
The other consequence of substandard service is that customers leave... this can also be highly effective, but shouldn't be threatned unless you can accept the consequences (maybe the grass isn't greener, the hassles of another setup etc.) I threatened to leave a while back and could almost see a rattle fly out of my pram...