no service problem iphone 7

kimia ~ Does your iPhone 7 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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If you've tried basic troubleshooting steps like restarting the phone or removing and reinserting your SIM card and the problem still happens, depending on when you got your iPhone 7 or what specific model number you have of it, you could be eligible for getting it repaired for no charge as mentioned in iPhone 7 Repair Program for "No Service" Issues - Apple Support.