how to stop 'butt calls'?

My phone keeps calling people. It had seemed to be when I had finished a call, phone would cal them back. Or phone would call first number in my favorites. But now it calls random people. Well, maybe not random, as it is usually just one of four or five most conmanly called people.

When it called first in favorites, I was able to insert another dead phone number in list.

Now it has stopped that, but other false calls keep happening.

Help!!!

phone is iPhone6s