Got a call from this number.

got a call from this number tried calling back to find out who was calling and it was busy wheni  finally got it to ring whoever it was just hung up and then it was busy again

Someone has called my cell phone from this number, when I attempt to call back it is busy for long periods of time.   This number rings again on my cell phone, I attempt to call back and there is no answer....how do I get it to stop.