what can be wrong in my car with the gas tank. on 2007 Chevrolet Equinox

when I put gas in my car the arrow goes up and down it doesn't show me how much gas is on the car.

Asked by for the 2007 Chevrolet Equinox
the fuel sending unit is bad, but they only come as a complete fuel cell. good delco part installed between 700.00 and 900.oo parts and labor