Answer and they hang up

They say hello, then hang up once they confirm a live number.

Just got call too said hello twice n they hing up.

My phone rang from this weird number. I picked it up, said hello twice and then someone came on. He said sorry, the transfer must not have gone through and to let him try it again. I said what transfer? Then he said oh sorry, how can I help you? I told him "you called me" and he told me that their phone system must be acting up, but how did they have my number in the first place?

Repeated calls from this number, disconnect once they are answered (ie automated dialer confirming my pickup I assume), attempt to call back number results in invalid number message/disconnected number message.