Noises During Shifting problems of the 2011 Hyundai Santa Fe

I purchased a Hyundai, not even one month ago. December 12th 2010. VIN [xxx] Hyundai Santa Fe 2011 it is supposed to get 20-26 miles per gallon. While driving the highway from florida to nc it got 15 miles to the gallon. On the way back the same thing. In addition the transmission was not right, the car would not shift and made a horrible noise several times. We did not think we would get home. It would not shift at all. I took it to the local Hyundai service center and reported it to Hyundai. They claim there is nothing wrong and that the car just needs to be broken in. I went on line and saw many consumers had the same complaints and Hyundai ignored theirs as well. I don't know where to turn. I never heard of a car needing to be broken in. The mileage is a lie. The car is not getting what they claim it should and others have reported the same thing to Hyundai. There appears to be a transmission problem with my car and with those of other consumers and they refuse to help. Can you help me please? information redacted pursuant to the freedom of information act (foia), 5 u. S. C. 552(b)(6).