Iphone SE gen 1 not delivering No Caller ID calls

Has anybody resolved this issue? Silence Unknown Callers is OFF but every time I get a telehealth call from a doctor using No Caller ID - the call isn't delivered. Sometimes shows on Missed Calls sometimes not. All software up to date. Though this issue has only started occurring in the last couple of months. Before that, there were no issues. She rings me by phone and then if the call gets through, we swop to Facetime on phone - could it be a Facetime issue? I have Facetime as well on my MacBook but don't use it to receive this call. It doesn't show up either on Facetime on Mac.