indentity theft worries

Maybe some of you can help me with my predicament.
I recently received a call from an 0800 number with a man saying that he was from Vodafone and offering 25 pounds credit for an agreement to extend my contract by 6 months. It sounded legit so I went along with it. I then had a change of heart and rang vodafone and asked them to cancel it. Of course they had no record of this exchange and didnt know of any offers resembling this. I am a little worried that this could be a case of identity theft.
The only information I gave to the guy was to tell him my name, my address, and my phone number.
The other explanation that has been suggested by my mates is that it could be a 3rd party mobile phone reseller trying to sell me an alternate contract. But I bought the phone and signed the contract in a Vodafone shop, so that seems unlikely. I checked my phone to see if I still had the 0800 number saved but alas, i has wiped it, and when I rang Vodafone they couldnt tell me what it was. Any idea how I can find out who this was?

Regards,
Ed

Hmm, that's pretty interesting. If you don't have the number anymore I can't think of any possible way that you could find out who was calling you.
And usually when a company is trying to do something with a contract they will do it in person or mail you something. Doesn't seem to make sense that they would call you. Sorry that happened to you.