No service on my iPhone
Ask your carrier for a new SIM.
The firmware on them changes over the years, so yours may well be long out of date now. 

[Knowledge source, recent similar issues &amp; similar cure]
My phone would drop the carrier network every few days, with a message that 'if this happens frequently, talk to your carrier.'
I did, they sent a new SIM, it's not misbehaved since. The 'old firmware' explanation was theirs, over the phone, so I have no documentary evidence.