I am unable to access cellular data on my iPhone 7

Abubakarmauwal ~ One possible reason for cellular network problems is a weak, aging battery. The antenna of your iPhone will then not be supplied with sufficient power to connect with cell tower signals. So...

Does your iPhone 7 still have its original battery?

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

Settings > Battery > Battery Health

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I found it was vpn turn of and then fix you vpn

It looks like your have already selected a Best Answer. That’s good because we cannot really help you research cellular networks in your country/area. This link may be a start, though —>> iPhone - Supported 5G and LTE networks - Apple

If you still need help and if I am misunderstanding your problem, then please read the article below then reply with pertinent information.

Writing an effective Apple Support Commun… - Apple Community