Inexplicable data usage messages

[KWall]

Got message from O2 Business on 14th Feb to say I had used 80% of my data, followed by a 100% message on the 15th even though I had turned off data. Told reset date was 7tj Mar (yesterday). Turned data on but received a message at 10.25am saying I had used 80%, followed by a message at 11.45am saying 100% used. I have never had an issue before and I actually use data far less than I ever did, as I am at home using WiFi majority of time. In any case I am not a heavy user generally. Help please.

[MI5]

@KWall 

Check the data use in your phone settings to see what's using it, but you'll need to call O2 on 8002 for any specific account related issues.

[KWall]

Thanks MI5. I will ring that number