Gas filling issues

[Colorado matt 0]

 I've been having a problem with putting gas in my 2017 chevy colorado z71 v6. Everytime I go to fill up and put nozzle on automatic, it doesn't work and spits out gas from the filler neck of my truck. I took it to the dealership twice for the same thing, the first time they said it was the charcoal canister and solenoid that got dirt and was needing to be replaced. When I tried to fill again, not only did the same thing happen but I had to pump gas very slowly just to get gas into my tank.

I took it back to the dealership again letting them know the problem was not fixed. They said that the check ball that's in the tank itself seized and that the only way to fix it was to replace the entire gas tank which would cost me around $2000. 

I was first wondering if anyone knows if there is a check ball in the gas tank and if it can seized or am I being taken for a ride?

Second if it truly is the check ball how can I replace it by myself without having to spend that amount of money that I don't have? Is there anywhere I can purchase the part(s)?

[newdude 2,270]

When you fill up your truck, is the key on or the engine on?  Or do you shut everything off then fill it?