This us probably a program called, calling multiple numbers one after another till someone picks up.. after a substantial delay.

It is often a debt collecting Agency or ... a fund-raising entity, oft ( maybe ) a charity such as Australian Surf-Lifesaving, which tries conning you to continually contribute a certain amount EACH month.

If they don't leave a message (they never do ) .. congratulations ... your instinct in NOT picking up .. was the right one! Label this number in your phone, "Do NOT answer"

I called back number (07) 3422 6549 rang once then goes to busy tone.