When you say Hello, the line goes dead. Then I recall the number, it answers with no identification and says we are busy currently leave your name and number and someone will contact you. I hung up of course .... But they keep calling!!

they hang up when I answer

When they identified themselves (Zoe), I told her I wasn't interested because (A) I'd had at least 30 calls from energy companies over the past two months and (B) was living in an apartment where we are locked into a contract for the whole complex, her words were: "Well, if you'd let me speak..." (and began to extoll the virtues of her business). I cut her off by saying "Sorry, did you really just say 'If you'd let me speak?'. She said "yes, if you'd give me a chance to actually talk"... I laughed and said "what???" at which point she said "Oh you f*ck" and hung up on me.

Called back on this number, went to voicemail but no identifying information was forthcoming. I blocked it.