I've never had trouble with DD for broadband; I just get an email to tell me the payment's due, my account gets debited - yes, I do check regularly - and that's that. It's true there was a lot of trouble with direct debits some years back - not just NTL, but a lot of companies - but it all seems to have been sorted out now.
In fact, at one point I wasn't being charged enough for BB; two payments for rather less than £24.99 were taken out, and it wasn't until I went through my inbox deleting old messages that I noticed the amounts and contacted NTL. The next payment was correct, and I wasn't charged for the deficit. They weren't allowed to, by UK law; if the DD says it's for such an amount, that's the only amount they're allowed to debit even if they've made a mistake and it's less than it should be. It's up the company applying the DD to notice and correct the error; I wasn't even obliged to tell them, but I have this annoying streak of honesty...
Oh well. If it comes to that, I'll just have to have yet another bill put on DD.