80 year old woman's iphone is not receiving calls nor text from a friend's number.

Hello, I am assisting an elder with a problem she has w/receiving a call or text on her iphone from a friend. I verified that the elder and her friend have the phone number of each correctly listed in their contacts. I know that the elder has the setting on to avoid receiving calls from strangers; but the friend's number is in her contacts and the friend has the elder's number in her contact correctly too. Last Thursday when I was with her, I noticed she needed to update her phone and she did in my presence so her phone is current with updates.

I see there's a question that someone cannot send nor receive messages to or from Android. I am waiting to hear back from the friend about whether her phone is Android or not. Does this matter at all?

I read too that if she cannot receive a call from a particular phone number, it could be she needs to contact her provider of service. Is this true?

So I informed this elder I would do the research to help her solve this problem as we cannot find the cause. I will see her late this week. Does anyone have a clue as to why? Thank you.