Any idea why this has happened?

I have a Samsung Tocco phone.
I put £10 credit on it last week and it has gone down to nil.
I haven't made any calls.
Any idea why this should happen?
Thanks as I am a bit dim where mobiles are concerned.
lissie

I put £10 credit on it last week and it has gone down to nil.
I haven't made any calls.
Any idea why this should happen?
Thanks as I am a bit dim where mobiles are concerned.
lissie

