Calls, stays on the line (listening) then hangs up .
The caller does this several times with out speaking , simply listening in as though waiting for the receiver to start talking or something...
then repeats several times, calling at different intervals NOT identifying themselves or as to why they are calling.
If the caller believes they have the wrong number then they should identify  themselves in  order to check to see if the the number they are calling is correct, however, when the caller does NOT do this, it is evident that the intentions of the caller is NOT a mistake NOR incorrect but instead to call and  harass the receiver for what ever reason making their negative actions completely inappropriate.