Hi @Davejj, welcome to our forum and I'm sorry to hear about this. 
Have you tried a different SIM card in the device? If you can borrow one from a friend, colleague or family member because it does sound like there is either something wrong with the SIM card reader, or the SIM card.
You could also try and perform a software repair using Xperia Companion to make sure that this is not caused by the software in the device as it will be reinstalled when performing the repair.
Do note that all data stored on the internal storage will be deleted, so creating a backup using Xperia Companion before you start with the repair is advised.
If the device is still not able to recognize the SIM card even after the software repair has been completed or with a different SIM card, please get in touch with your Local support team as the device will need to be examined at an authorized service centre and they will assist you further with this.
Let me know how it went!
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