I have the same problem. I answered once at 3am without looking at my phone, thinking someone was in trouble and had this weird breathing/crying sounds. After I hung up it immediately called back (too fast for a person to have dialed again). Later I received 27 nonstop calls from an unkown name which I had added to my reject list. Every few weeks this happens, but since I have them on my reject list I don't actually get the calls(just see them in my phone history).