Heaters fail. It will happen. I've got a Marineland that has failed on. Just like yours. It's why I always recommend 2 heaters at just over half the wattage required for a tank. When the heater fails since it's a lower wattage it can't overheat the tank if it fails on. If it fails off the other heater can at least keep the tank from going too cold.
Would be nice if the company stood by their product but yeah, guessing its not likely :/
They give their products a warranty. If it's within that period I have no doubt they would replace the product. No company will replace the livestock though. How long after the warranty period expires should they have to replace it then so they "stand by their product"?