is this the car that had the engine replaced? They probably squished the heater core tube when removing the hose. I’ve done it on accident once or twice. Unless you can prove that you might be hooped. Unless someone has a better explanation? I don’t see physical damage being covered by warranty, unless it came from factory like that(doubtful)
Myself I’d to make the tube round and seal, make sticking a smaller diameter piece of pipe into the tube or figure something out.
Worst case replace the heater hose from where ever it starts, through the firewall and eliminate the tube that’s damaged. Just cut it under the dash and hook the hose to it. This is a terrible explanation but cheap fix to simple problem.