Rings me several times a day but leaves no message very annoying when ringing the number back it just rings out - Moved to my blocked list

saying they are from optus but its not an optus number. at 1st it say pro group or prode group.... be careful if you give out imformation

They have taken to calling me 3 times a day. I don;t know who it is, but given I don't know anyone in SA, I'm guessing it's a scam.

Instant hang up first time, second sounded like a fax or modem handshake with massive static that forced an HTC One m9 to restart (Although then I was at 4% battery)