iPhone SE occasionally won't receive calls, I get missed call notification instead

At first I didn't think that was such a big problem, because it happened only every now and then, but now it's becoming frustrating, because I missed some important calls because of it. Long story short: Sometimes I simply won't receive a call, instead I get a missed call notification, sometimes even few minutes after I was called. 'Do not disturb' is turned off, so that cannot be a problem. Sometimes I don't receive a call even while using a phone. Has anyone else had such problems before?

Kind regards

Solution 1:

It's probably worth rebooting the phone, just in case, & checking your carrier settings are up to date [Settings > General > About] but ultimately I'd speak to your carrier.

I had a similar issue last year which was resolved by getting a new SIM. Apparently, I'd had the old one so long I was several firmware generations behind & the new card just fixed it immediately.