UPDATE: Total turn-around! after refusing to come at first, a person from the automobiles store where maintenance of the car is undertaken, showed up a while ago. he said that mice have chewn off some wires. the earlier person who was called (a battery-store guy, who was called in suspecting that the battery was at fault) had said that the battery is fine, and headed to check the fuel-tank with a pipe, and then declared that the tank is empty, indicating that there has been fuel-theft. after he left, 2L. of petrol was bought, and when it was being put in the tank, the tank started overflowing, meaning that there hadn't been any theft, and the tank was full with fuel!
makes for a nice Sunday-satire! sorry to bother you all.
mod, you may please close this thread.