Stopping credit being used up

Hi
Im new to the world of android phones. What is happening is when i am at work and not near a wireless signal my credit just goes in minutes. Is this apps running in the background and using a mobile signal to update, etc. How do i stop my credit being used up when i am at work and not using the internet or apps on the phone, i just need to make, receive calls and texts nothing else.
Cheers
Lee

 

Hi Its a alcatel ot 980.
Sorry forgot to put that bit in!
Cheers
Lee