Heater Inlet hose...how to remove

2000 5.3 z71.

Heater inlet hose bused and truck subsequeny overheated.

This is the separate hose / different from the main assembly. My question is how to remove the bracket near the firewall. It's a plastic assembly that the hose fits inside of. I've twisted, turned and bloodied my knuckles...still won't come off...

Thanks.