Hello, I sought answer from Xperia Support on the same issue and they sent me this reply:
Try these methods one after the other. Verify whether the problem was solved after each method, before trying the next one.
- Make sure that you did insert the SIM card the prescribed way into the correct slot. You can look up the correct way to insert your SIM card in the user manual for your Xperia™ device. You can check the online user guide for your product on www.sonymobile.com/global-en/support/ - just select your product and click Online user guide.
- Check that you did you use the correct SIM card format. Different Xperia™ phones or tablets might support different SIM card formats: Mini SIM (a normal SIM card) or Micro SIM (very small SIM cards). Please do not use a micro SIM card or a Nano SIM card in an adapter for a larger format. Not only can this interfere with the detection of the SIM card, but it can also physically damage your SIM card holder.
- If your Xperia™ phone or tablet uses a Micro SIM card or Nano SIM card, check if you used a punched out Micro SIM card or a punched out Nano SIM card. If you have converted your Mini SIM card to a Micro SIM by stamping it out the SIM card might be defective due to this process. Please test out a original Micro SIM card in your Xperia phone or tablet to rule out that possibility. Note, that testing the punched out SIM card in another device does not rule out a defect, as different devices might react differently to a defect of the SIM card.
- Check how old your SIM card is. Previous SIM card formats used different voltages. If your card is older than 4-5 years please contact your network operator to swap your SIM card.
- Check if your Xperia™ device works with another SIM card since your SIM card might be defective. Testing your SIM card in another device does not rule out a defect of the SIM card, as different devices might react differently to a defect of the SIM card.
- Make sure that your SIM card is activated. If your SIM card is new it might take a while until you can use it in your Xperia™ device. Contact your network operator if you are not sure if your SIM card has been activated or not.
- Update your Xperia™ device to the newest software version. Due to improvements in newer software versions it might be necessary to update your Xperia phone or tablet to the newest available software version. (See the related articles for a guide on how to update your phone or tablet software.)
