Iphone 12 Activation failed

Bought a new iphone 12 and was setting it up but "activation failed" error pops up. The error reads ' This iphone is not able to complete the activation process. Please visit your nearest Apple store or Authorised service provider for more information or a replacement" I tried contacting apple helpline which asks for serial number/ IMEI before but it also didn't recognized serial number I mentioned on box. Please anyone help in resolving this issue.