I know that you have to do

go to the spare part outlet. Ask the lady for the petrol level sensor with is located inside the fuel tank. I forgot how much it costs but make sure it is the one with the circuit contact. The earlier ones did not have the circuit contact. It's kinda long and thin, looks like a metal coat hanger, has a stopper on one end and a buoyancy unit at the other end in the middle is the circuit contact. Now all you have to do is use a pipe to drain all the fuel from the tank, remove the seat, remove the screw that hold the tank, remove the tank, turn it upside down, remove the screws that holds the petrol level sensor, the whole thing will come out. Now put the new one and do the all rest of the fitting.
Your problem is your petrol level sensor inside the tank is damaged. I don't think your warranty covers it though. I know it a real pain and bother to do repair stuff like these yourself, but it'll help you understand your bike better. Or you can just ask one of the service center guys to do it. Problem is they are careless, scratch stuff in your bike etc. I personally really hate them.