I think it will be down to the terms of service and the agreement you signed that you agreed to give 30 days or a months written notice to terminate the service, this will be irrespective of whether the contract is still in force or not.(but usually you're not allowed to cancel within the contract)

It will be under the cancellation terms in your agreement, had you given this written notice on 7th Sept then it would have coincided with the same date the contract ended 7th Oct.

Hi,

I took out an 18mth contract with vodafone, 18mths meaning it was due to expire 6th October. I phoned them approx a week ago and was advised to send confirmation in writing. I have just received a telephone call from them and they advised that my contract will end on 7th November as this is a month from the date they received the letter.

What i dont understand is why i need to confirm in writing when the contract is eighteen months?????