Unable to get hold of a Qantas agent

I have a ticket credit that i am trying to use to book a flight, I have been phoning for days for hours with no luck of reaching an agent. Last week Friday 25/03/2022 and agent phoned me and I booked my flights then the Monday 28/03/2022 I got an email notification that my flight date has changed and I can go online and confirm this, which I am unable to do as it wont allow me to do anything online as my ticket credit is from 2020. I queried this and finally after 2 days got an answer that it was the fault of Qantas. Now i am trying to change my dates to book my flight and I cannot get hold of anybody telephonically or email. And because this was a ticket credit from 2020 I am unable to confirm or book online. This is extremely frustrating and poor service regardless of high volumes of calls. Does Qantas expect us to sit a full day on the phone while we have jobs to do as well. I am even now considering going to the airport to see if they cannot assist. I have been trying since last week to Book my flights, I am shocked that it takes soo long to book a flight.