when you do a call back, Optus advises that the number you dialed (08) 6902 8628 has been disconnected.

this number constantly calls daily the same time and no one answers and they hang up when you ring it back it says it is disconnected

Have had many calls from this number recently. no answer when I return the call.

about some power company

I don’t bother answering any more it’s spam I block and they call from a different number

Spam

Phone rings - when you pick up, they hang up immediately. It's like a call center where people may be measured on the number of calls they make, rather than length of call. So they hang up immediately so they can dial more numbers in a given period of time.
Some days, they ring several times over a number of hours. I've had their telephone number - 08 6902 8628 - blocked by my telephone service provider, Telstra - I asked Telstra to check the name of the number owner/organization - they checked, but because it's not a Telstra provided number, they didn't have access to the name & couldn't confirm name. So the number is provided by another telephone service provider, other than by Telstra.

Spam, rang back number and it's not connected.

daily call at same time. no one answers and they hang up

I called back number (08) 6902 8628 rang 2 times then goes to busy tone.