I had a weird occurrence this week. I hadn't updated my CC info after getting a new card with new expiration date. I got an email that said my renewal failed. I logged in on the phone and updated my CC info with about 40 minutes before my unlimited plan expired. Well, when the 40 minutes was up my cellular data went dead. I did troubleshooting. Nothing helped. That night, I spent about 2 hours on chat and tech support. Apparently, the SIM refused the update, and I needed a new SIM. So I went to the ATT store, where they quickly replaced the SIM. The employee who helped me indicated that there have been several cases where the Apple SIM had issues. I don't know whether getting close to end of plan contributed. It was the first renewal after transitioning my plan from my old iPad to my Mini 4.