Well, Im just going to put this out there and say that YES, I am an idiot.
So it's my daughters car, and I've been thinking that she has been putting fuel in this car for years, so obviously she knows how and it was indeed full everytime she said it was. I also put fuel in it and considered it was full but the guage showed half a tank. This indeed isn't the issue, the sending unit is working fine, I used a meter and ohmed it out and even was able to take the car to a different station and fill it all the way up and the gauge worked fine and showed full.
Fast forward a few tanks and I get a call that the car will not fill up again, so now that I know the sending unit is working, and that in fact when you try to fill it, it fills up the neck of the tank and makes the pump shut off, thus not allowing any more fuel to enter the tank, leading me to believe i have a valve problem such as a fuel tank vent valve type of thing or Vapor Canister that could cause this? Does anyone have any knowledge of this system or a valid diagram? 2011 Optima EX Korean Made.