£750 bill from Vodafone as iPhone sent 20GB last month, please help!

Question

Hi
I have just received a shock data bill from vodafone. Apparently my iPhone has been using between 500 MB - 1GB a day for the last month.
I have had the phone for almost 18 months and cannot work out why this has suddenly happened. I have not downloaded a new app or changed my usage at all.
I checked the phone and it states that it has sent 20.7 GB of data, and received 1.7 since last reset (October).
I only use the phone for calls, texts, and social networking. I have wifi at home and barely use cellular data.
I contacted Vodafone as I wish to dispute the bill (I am happy to pay for what I have used, but I cannot see how I have used this!)
They state that if I can show it is a software issue, they will write off the £750. At first they suggested I send it to them and they would check if it was software or a fault, until they realised it was out of warranty, then they said they can't look at it unless I pay £150.
They suggested giving apple a call, but I looked on website and to call them will be £25 and I am not sure if it will resolve the issue.
What can I do? The phone is still on iOS 6.0, I realise the data issue could possibly be resolved by updating, but am reluctant to do this before the phone is checked out (if I can get apple to check it out). For the time being I have restricted all data to wifi.
Is it likely to be a fault/software issue? I have not sent any files anywhere etc. If I drive to my nearest apple store (at least an hour away) will they look at it/are they likely to help/admit it is software and give me some proof for vodafone?
Please help!!

Answer 1

Contact the Apple store directly (or Verizon) as Apple (nor Verizon for that matter) monitor these forums.