My iphone 7 has "cellular error " and the network has no service what can be the problem

This may be relevant:

iPhone 7 Repair Program for "No Service" Issues

Does your iPhone 7 still have its original battery?

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

Settings > Battery > Battery Health

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Who is your cellular carrier? ATT? Verizon? etc.

You need to contact them to resolve this issue, which may possibly involve information in the link below if you still have an iPhone 7.

iPhone 7 Repair Program for "No Service" Issues