Phantom cell usage.

Can anyone give advice on trouble shooting my "phantom cell usage".

I keep coming inside, to find that my phone, which is NOT been used, has received texts from Telecom, telling me, that I have just blown thru my 10 mb daily quota !

I have the "netusage app" which appears to be a load of ar$e as it hasnt shown ANY cell usage since I installed it, about a month ago. It is picking up wifi usuage, but I couldbt vouch for its accuracy.

The phone has wifi enabled, but on occaision it can lose it, and it needs to be restarted (the wifi).

I have removed the most recent apps I installed to see if helps, (Pulse, and Linux/Unix News app).
Its a Samsung Galaxy 5.

Cheers Jeff