Rusting Jet Chef Microwave

Bought a Jet Chef Microwave less than 2 years ago for R4500, receiving a 2-year warranty. It started showing rust marks on the interior (stainless steel) recently. When I complained about it, was told that it is a "maintenance issue" and is not covered under their warranty. Been told that I should try rust removing products! Pathetic product and service, will never buy Whirlpool again.