A320 flight crew reported an aircraft swap after maintenance could not accurately determine the accuracy of the fuel quantity gauges or the actual fuel load on board.

Narrative

Crew was preparing to depart ZZZ on schedule when it was discovered the aircraft had been over fueled by 1;000 pounds. when the fuel sheet was consulted; it showed the aircraft fueled within tolerance at -60 gallons. This made no sense as an over fueled situation should mean the fueler filled to aircraft with more fuel than planned rather than less. Fueler's math was verified by flight crew. Pre-fueling FOB on fuel sheet corresponded exactly with what the block in fuel was on ACARS and the amount of fuel on the flight deck gauges corresponded exactly to what the fuel sheet said was on board; 23.0; which was 1;000 pounds over.A new flight plan was requested from Dispatch with the new heavier gross weight due to the extra fuel. This generated a new fuel slip with the higher fuel load. This led [to] problems later.Crew suspected a gauge error and wrote up the aircraft requesting the tanks be sticked to determine the proper amount of fuel on board. Passengers were de-boarded due to the time and cold aircraft.Maintenance verified the proper density; which was what was on the fuel sheet; and verified the math that the aircraft appeared over fueled. The tanks were sticked and it was determined that the left inboard gauge was in error and out of tolerance indicating nearly 1;000 pounds more than was actually in the tank. This was an acceptable situation per the MEL and left main inboard indicator was deferred. Passengers were boarded again. Crew prepared to depart again and the fueler showed up and put more fuel on the aircraft per the previously requested flight plan.Per the MEL; to verify the fuel in the left main; a tank stick was requested again. When this stick was done by ZZZ Maintenance; both inboard main tank gauges were discovered to be reading higher than the actual fuel on board by over 700 pounds; a combined nearly 1;500 pound error with all the implications of the crew not having as much fuel on board as planned and bad weather forecasted for the return to ZZZ in the same aircraft. Also; the MEL requires the opposite main tank gauge to work correctly and that was now in question.Maintenance then chose first try to reset the via pulling circuit breakers the fuel quantity indicating computer. This was unsuccessful. They then tried to try to replace the fuel quantity indication computer; but I have no idea how that turned out since after over 5 hours of delays; the Operations Manager ordered an aircraft swap.