Thank you for reaching out and letting us know about this issue. I am more than happy to help. Given the content of the notification, the device and the SIM card seem to be having an issue communicating with one another. Those types of notifications will also arise if the SIM card is being used on an unsolicited device.
If the SIM card is being used with the official mobile device on your account, I would recommend removing the SIM card and re-inserting it. This will prompt a network update on the device. In case you have already done this to no avail, the next step would be to have the SIM card replaced.
You can send me a private message by clicking on my name ComcastChrisL and then click send message. Please include your first and last name, full service address, mobile number, and last 4 digits of the stored payment method on file. Once I authenticate the account, I can send you a new SIM card.
Additionally, I’ve added the following link that includes an additional link so that you may locate the closest Xfinity store to you; https://www.xfinity.com/mobile/support/article/xfinity-mobile-stores. Finally, you can call our customer support service line and have one sent to you that way - 1 (800) 934-6489.
Let me know how you want to proceed.