Hi AbbaTKA,
Thank you for using the Apple Support Communities. I understand you may be having an issue with a cellular network.
To clarify, the "vf" you see is likely referring to VodaFone, so it sounds like your device is connected or attempting to connect to that network. Do you see the same "vf" at the top of your iPhone display, or are you seeing a "No Service" message? If you are, I recommend giving the troubleshooting steps here a try: If you see No Service or Searching on your iPhone or iPad.
On the other hand, if you're seeing an alert that your SIM isn't recognized, the steps in this link are a great place to start: If you get an alert about the SIM card in your iPhone.
I hope these links are helpful.
Have a great day.