Transmission Stuck In Gear problems of the 2008 Kia Motor Spectra

I test drove the vehicle and it drove fine. After I signed papers to buy the vehicle, I drove it home. On the way home I was doing the speed limit which is 65mph but I always stay a little under that speed limit. I got to about 65 and boom it was like the transmission had come through the floor and it felt as if I was going to be ejected from the car! that scared me to death!!! after that it started dragging so I had to exit the highway and drive the city streets with my emergency flashers on because I could do no more than 35-40 mph. I got the car Nov 2016 and this happens everytime I drive it. Its doing the same thing just sitting in a drive through. It kicks back so hard it hurts my neck. It feels like someone hits me from the back everytime. I would really y like to know where I can have this repair taken care of because this is very dangerous. I have read a lot of reviews online and a lot of people have the same issue. It's been doing it since day one and I need it fixed because it hurts really bad. I didn't do this to the vehicle. It happens no matter what speed you're doing and then acts like it's stuck in high gear and takes off slowly after it jerks.