Gilera DNA 50 Speedo Problem!?

i recently bought a gilera dna 50, on the speedo it said i had nearly a full tank of petrol and i had no oil, i put 2T oil in and it still said there was no oil in the tank. i left the petrol because it said there was some in it. i was riding my bike for about 2 days before my petrol light came on even though the gauge said i still had half a tank left! i got home and put a bit of rubber tube down the petrol tank and it came out dry. so the lights that come on are right but the 2 gauges at the side arn't! any ideas how to fix this?