2021 Ram 3500 Visibility problems

my truck has approx. 80,000 have been dealing with the dealer for at 3 months he says the heater core is clogged do to the type of antifreeze required to use. They flushed the system still the same blows luke warm air Will not keep windshields clear during bad weather They say heater core needs replaced and not covered under warranty my thoughts how can heater core be clogged on a truck less than 2 years old and 80,000 miles have made several complaints can get exact dates of first incident and have receipt on flushing No one else besides dealer has ever worked on truck