My iPhone 6 is blocking numbers randomly on its own

Last year my phone was making calls on its own and I noticed I was not getting calls, text and voice messages from many people . I found the problem by talking with apple support. My phone is blocking numbers randomly -On its own! Sometimes those number are the people in my contacts , sometimes new numbers and sometimes people missed calls from or dialed recently . I had to go to Settings/Facetime/ blocked and unblock people , numbers every 2 hours or more often . Blocked numbers would appear in front of my eyes , right after I deleted them from Blocked .

My phone was 4 months old , I went to apple store and was told my phone must have some hardware issue. It was replaced on a new , same iPhone 6. The only things were trasfered were my pictures via airdrop . I was happy and though my nightmare is over but NO...

New phone was acting normally and then it started to behave the same . The only difference - it was not making calls on its own. New phone is blocking numbers from my phonebook , missed , dialed , new called numbers -unidentified . My nightmare is back !!! It doesn’t block all of them , just randomly picks numbers.

I called Apple Tech like 50 times in the past 2 months and we tried to make sure my software up to date , delete/ erase my phone and download from the back up , erase and start as new, connect to the computer / iTunes / download a new software there ( it was not available on the phone ), erase and start again/. I went to Att&T and changed my sim card. It was not blocking anyone for 2/3 days and then got back in to the old mode - blocking .

My son has the same phone and using my iCloud , his is less capacity , he doesn’t have this problem . I do not think phone is a problem itself , as I have a new phone with the same odd issue. The only think in common between those phone is my log in to I cloud with my email , it downloaded my phone book. In the process of erasing my phone many time , I deleted all my pictures and apps . Started as new and used my email ( I had on my other phone ) to set up this new phone , as I need my contacts . I did not download anything else .

Phone is blocking on average 10-15 numbers , every 2 hours. I don’t know when and how , I just go to that setting every moment I got to take those numbers off the block list .Click Edit and Delete from Setting/ Facetime/Blocked or Phone / Blocked . I have iPhone 6. Model Number NG4R2LL/A, Version 9.2.1 (13D15),128GB Capacity . Apple Tech Case Number 1045129693 - I hope someone from Apple tech will read this and help!!!

I am so frustrated , all those steps were taking in 2 months period , I call , speak with tech support , wait , offered steps to take , wait till next day or 2 to see if it would block , call back again , speak with Senior Advisors , some never called me back or made any notes I called , as when I call back no notes were seen . Left those Senior Advisors voice messages and emailed , no help or respond My phone is still blocking people ...numbers ...

Please help !!!!