iPhone 5 using excessive data

Hi,

Is anyone else having problems with data usage on the iphone 5? I purchased the iphone 5 in October 2012 and had no problems with data usage. I then lost my phone and got a replacement through insurance in June 2013 and since then i have exceeded my data limit each month.

I used 24 GB in July and crossed my 15 GB limit in August and this has never happened before. I'm not doing anything differently (previously I used 1-2 GB per month). I've had to pay 2 huge bills of €300 per month as my service provider says I have used all of this data.

Can anyone help please?