@Jade_S Thanks for the updates, though I seemed to have suffered none. 😊
Adding to what @softech has suggested, please consider adding a 'Services Status' page to PM's website displaying the current status of services. This should be the web page every user should visit first before troubleshooting further. Below is an example of another service provider's status page (name blanked out) as sample.
@hari_pm Try to connect your phone to a computer and start iTune to download all the updates and carrier updates and see if it works.
If it still not work, you might have to try a Network Refresh to see if it fixes the issue
I used itunes to update the phone and restore it from a backup, does that process not include a network refresh?
I don't think that it would do a network reset. Network reset will reset all your stored wifi passwords, etc.
Might be an issue with iPhone 8, since another poster earlier has the same issue but was able to insert their SIM card in another phone and it worked.