New SIM and provider, old number transferred but new number still in iPhone

Hi I changed my provider keeping my old number and old phone. The number has transferred but when I check my number in my phone it’s the new sim number. It’s the same in IMessages and face time too. My provider told

me to go

to Settings-reset- reset network settings. I’m worried if I press reset it will just reset my phone I will lose everything. Can someone please help. If I press reset what comes up? I daren’t press it. Thanks

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