Data allowance gone in one day despite using wifi

[Whaleman]

Hi,

On average I use only about a third of my monthly allowance. It renews on the 4th of the month. This month, the following day I received a message saying I had used up 80% of my allowance, now it has all gone.

I've been at home all this time, using wifi on the phone. How could all this data have been used in just a couple of days? I don't want to buy a bolt on in case there is a problem and the same thing happens.

Thanks

[MI5]

@Whaleman 

You need to turn data off when using wifi.

If it drops out, your data will be used instead.

[jonsie]

You would be better off turning off mobile data when on wifi @Whaleman 

[Whaleman]

Thanks.

Yes, I should have added that I haven't used my phone in the last couple of days either.

I can't figure why 3x as much data has been used in just two days than would normally be used in 30 (and being at home I would have thought my data usage would go down if anything). Strange.