After updating iOS to the latest version I am unable to call as it says no network service
Remove and reinsert the SIM.
Toggle Airplane mode on and back off.
Settings > General > Reset > Reset Network Settings
Basic troubleshooting from the User's Guide is reset, restart, restore (first from backup then as new).
I did all those steps except restoring to factory setting. Network service comes and goes back to no service. Again when I entered my phones serial no it says it is the no of replaced product. Does it mean that I bought used phone?
Restore as new.
Yes, the device was replaced by Apple for the original owner and somehow made it back into the supply chain with Apples approval.
Return it to whomever you purchased it from, if still in the return period, and demand a refund.
I bought from MBK Mall in Bangkok, Thailand about 3 months earlier and paid 600 dollars. I am from Bhutan . It means my phone will not work now?
Take the issue up with the reseller.
actually i lost my bill, so can i take my phone to any apple service provider?
No one cares if you have a receipt.
If you have a hardware issue, take the device to Apple or whomever provides support in your country.
Warranty and support is tied to the device, not the original purchaser.
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