Did you plug in the headphone to the correct 3.5" connector of the TV? Some might have more than one of these similar connections.
Do the wireless headphones have a 3.5" connector? Which headphones are you using?
Raise the volume while the headphones are connected.
Which kogan 49''inch smart tv are you using? This one?
https

/www.kogan.com/au/buy/kogan-49-smart-hdr-4k-led-tv-series-8-mu8010/