Your phone will use the Internet if it's available. It periodically checks for updates. The only way to prevent this is to turn off mobile data, but some people have reported that their account is still showing as using data even with mobile data off
you don't say whether your bill shows a charge for internet usage?
If this is the case without you using the internet then it most likely will be as Gorf says. "Smart phones" connect to the internet automatically to update systems & Apps (it will show as small amounts KB of data).
If this is the case & it is costing you. You need to turn off/disable mobile data.
If you are unsure how to do this, tell us the make & model of your phone & I'm sure someone here can help.
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