Bests & Worsts Reviews from Amazon

I read good reviews and bought this back in December. My baby was born 2 weeks ago and just started using it. I have been using it about 3-4 times daily for the past 9 days, and I really dont know what to do about the brown stain on the heating plate. The instruction manual says to pour white vinegar and water until the limescale has dissolved. My second photo was taken after I left the solution in the heating pad for an hour. The manual says the dryer should be descaled at least once a week. Ummm...I do this once a day and it still looks like this. And the stain is permanent. I dont know if this is safe to use for my newborn at this point. What a disappointment.