Random data spikes on iphone 5?

I have an iphone 5 and the carrier is verizon, I'm not sure how this whole data thing works but I get a text message almost every other week saying I exceeded my data limit or that I've reached 50% of it 75% of it and so on, I turned my cellular data off, deleted some apps, and some pictures and I keep getting a message that says I used 50% of my data allowance for the month, which I don't understand because I only turn my cellular data on when I'm outside, and then switch to strictly Wi-Fi when I'm in the house, is the cellular data still in usage while I'm using Wi-Fi? I also share a data plan with 2 other people who live with me, could it be that they're using too much data which causes my data to randomly spike up? How can I stop the data from randomly increasing?

Yes. It's not necessarily you that's using the data. It could very well be the people that are sharing the plan with you. You may want to sign into your online My Verizon account and look at the activity. You can see who is using the most web and features. You can also call Verizon at 1-800-922-0204 and they can look into the problem for you if you don't have a MYVERIZON account.

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