Caller: Heavy Breather

This person (maybe telemarketer trying to get credit for connected call and time spent but doesn't say anything ) - you can hear background noise of breathing. They called our business line in Perth Western Australia 5 times in a row but said nothing, silence, immediate hang up and heavy breathing. The last call we received I said "if you do not id yourself we will block this number" I got more heavy breathing, then they hung up - and they haven't called back today.