Calls multiple times, I never answer & they never leave a message

seemed to be selling something - hung up quick - rang a do not call number

Called back, only heard a loud ringing tone, a couple of clicks, then a goodbye before disconnecting.

Caller: Call centre trying to sell power services

Got quite aggressive.
Would not answer my question about why they are calling me.
Blocked.

ii called back and it rand like i was standing in the room of the ringing phone.. anyway after a bit a recorded voice said "good bye".. god these calls need to F off.!!!!

I called back number (03) 8202 5430 spoke to a guy who said I've reached Benefit Deal.

Called twice within 45mins.
Rang back (hint, if calling from a mobile, dial 1831 before the number to hide your mobile number) and spoke to an indian guy named 'Charlie'. Said that it was something to with regulatory changes to smart meters and they needed to speak to the person responsible for the bills.
Asked a few times what organisation he was with and never got an answer, just kept repeating that he needed to speak to the person responsible for electricity bills and the smart meter because they have to talk about the legislated regulatory changes.

Still no idea as to who the company is so can't tell if it's legit or if it's some kind of scam.