Why is my I phone 5 c using all my credit when I don't call text and mobile data is off?

I topped up £10 last week and my balance is now at £1.80 when I havent texted or called anyone and my mobile data is 110% off or:I topped up \u00a310

I topped up £10 last week and my balance is now at £1.80 when I haven't texted or called anyone and my mobile data is 110% off

or:I topped up \u00a310 last week and my balance is now at \u00a31.80 when I haven't texted or called anyone and my mobile data is 110% off

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