I'm with Vodafone and I found myself in a negotiating position in a rather unusual way - my contract with them is only 3 months old.
Back in mid-December I set up a new 18-month contract with Vodafone with 200 mins any time, any network, 'Stop The Clock', and 500 free texts per month. The normal cost per month was £30 but for the first 3 months I was to pay half-price line rental, i.e. £15.
At the time I entered my bank details onto their site to set up a Direct Debit for bill payment. However at the end of February I checked my account online only to notice that payment had not been taken by Direct Debit for the first 2 months, leaving me with an unpaid balance of over £40. I checked with my bank and the D/D hadn't been set up. So I rang Vodafone to enquire and they said that although the money had not been taken at this stage they would "re-present" the D/D again and take the balance. I was happy with this as it was what I'd roughly been paying per month with 3, my previous (rubbish) provider.
At the beginning of March I received a letter from Vodafone saying that my D/D had finally been set up, over 2½ months later. But then I turned my phone on the next day only to find that it didn't work! That morning in the post I received another Vodafone letter stating that I had an overdue balance on my account (just over £40, surprise), and my line had been suspended pending payment.
"Right," I thought - "this is all your fault and I resent being threatened, let alone disconnected when it was no fault of my own!" I rang customer services from a landline and very calmly pointed out the problem. I also paid the balance by debit card and was immediately reconnected.
But I wasn't going to stop there. I (again, quite good-naturedly) accused them of poor organisation, saying that the D/D should have been set up in the first week of my account's operation. They spun me a story, saying that the D/D had been started with the bank about 2 weeks previously. I replied that if that was the case, it would have been in place by the time my bill was due! They replied that it could take 10 working days to set up, and that I'd need to check with my bank. So I took the guy's name and number, and said I'd check with the bank. Surprise - they'd only received the D/D instruction a week previously, but it was now in place.
So when I phoned back the rep I explained this. He stuck to the 10 day story, refuting what my own bank had just told me! I said I was not happy and that I would like some recompense for the situation, in particular being sent a threatening letter and being cut off through Vodafone's own incompetence. I kept the smile in my voice. He fetched a supervisor.
The supervisor immediately apologised profusely. This wasn't good enough, the D/D should have been set up much sooner, I shouldn't have been cut off, and so forth. I said I was happy to accept the apology but added, "When I tell my friends about this I'd like to be able to say that Vodafone did something to put the situation right." I asked for another 3 months' half-price line rental - and immediately got it! I only wished I'd asked for 6 or 9!
A small victory but a sweet one nevertheless! I based my argument on their reputation rather than their need to retain my custom, but it still worked.