Apr 23, 2015

Can someone use my phone data without my knowledge?

Last January I bought an iPhone 5 second hand and ever since then my phone bill has over doubled.i would like to know if the person I bought it off ,who I didn't know,could hack in and use my data as its all internet usage that's putting my bill up and i really don't think I'm using it anymore than before.if so is there any way of stopping this happening?
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