I called back number (08) 7100 1205 rang once then goes to busy tone.

this number calling on the average of 5 times per day , no answer on pickup , have rang back but continually engaged, have emailed Telstra ,will post any outcome

Keep calling and hang up when I answer

First call took a while to connect and the caller sounded like they were standing in the middle of a busy road in Mumbai. They were trying to sell some government retirement incentive. I told them that I wasn't interested and they rang back the following day.

Missed 2 calls went to ring back but engaged or nothing?

keep calling and then they hang up when I answer