Called me also & they hung-up after a few rings, who are they ?

I just received a call of a few rings, and they hung before I could answer.  They called back about 30 minutes later and no one was there when I answered.  Telemarketers with a poor autodialer?

fraud spammer

rang three times then hung up

left pic email which then rings their number and you are told to hold...   I hung up
there is no identification name anyplace