How do I stop my iPhone from auto blocking saved hospital contacts?

I’m working as a doctor. On days that I’m on duty, the hospital will call me to see a patient when they are having a medical problem (usually emergency cases like cardiac arrest, or respiratory distress). Last week one of the nurses told me they can’t call me through my phone. Turns out my iPhone blocks ALL the HOSPITAL calls. So if the nurse use her personal phone, she could call me. But if she used ANY of the hospital phones (she tried with 8 different hospital number), she couldn’t reach me. I found out that my phone automatically blocked the hospital contacts (which were SAVED IN MY CONTACTS) and unblocked them. And then they get blocked again almost everyday! Every morning I have to check the “blocked number”, unblocks them, and then in the evening they are block again. This is dangerous because if there was an emergency case like cardiac arrest but the nurse couldn’t call me in time, the patient could die! Please help me fix this!

P.S. I do not have any third party app. I have also turned block unknown calls off. As I mentioned, the hospital numbers are saved in my contact, yet they were blocked!

[Re-Titled by Moderator]