OK.
The guys werent being facetious, it does take a while for the gauge to move from full. It sounds like your fuel transmitter is stuck. sounds like you will need to pull the fuel pump/sender assy out of the tank ( it comes out the top) and have a look. If it has gone bad, it might be repaireable, or it may need to be replaced.
In the mean time, fill the tank, reset the odometer and refill at around 400 Ks