I got same sort of issue...

I am a Vodafone customer nearly 14 months, I am not internet person to use my mobile for surfing internet, I always used below monthly allocated 1.5 GB free data so pay my cap money only, suddenly I got bill for last month approx $ 450 that to interestingly for 2 days data usage in that month. I have called Vodafone why this is happened to find out are there any glitch in network, because I can not pay and accept this usage which I didn’t used, they are offering 50% still I am not happy as I didn’t used at all how would I can accept, finally they said we need to investigation finger crossed positive outcome.

I have a iPhone4 and have been using it for the last several months. I am a reasonable user of it like looking internet and some Youtube download one to two hours as maximum but am definitely not heavy user. I have a contract with Vodapone as a $59.65 package, which should be more than enough to cover my reasonable usage until last month. However, I almost fainted when I received a monthly statement from Vodapone recently, it shows more than $300 worth usage. I looked carefully the details of my statement through and noticed my usage was like 300 to 400MB daily. So I made a call to Vodapone and asked for investigation. They said to me even downloading 5 minutes video from Youtube, it could be like 1GB size. iPhone also updates its software automatically even while you're not using, therefore I have to accept the usage and pay for it although they will investigate it anyway.
All I have to do now is my fingers crossed and wait and see what outcomes but I'm wondering, is there any ways of proving my previous usage through my iPhone?