Pawan, it's not entirely clear what's going on with your car, so hopefully we can clear it up so we can help you. It may be a translation issue, but I don't quite understand your question.
First of all, what do you mean when you say your oil is "finished"? You seem to be implying that your engine oil is used up or something, but it's not clear exactly what makes you think that. Oil doesn't simply degrade in a month to the point where it's unusable, and there's no indicator light on the car that purports to report on the condition of the oil.
There is a warning light on the dashboard that indicates when the oil pressure is reading low. If the pressure goes too low the warning light will either start flashing, turn red, or both. So are you saying a month after an oil change the low oil warning light comes on?
If that's the case there could be several explanations for that. A worn oil pump, defective pressure sensor, oil leak, worn piston rings are all examples of things that can affect oil pressure.
If we can clarify your question then we can pursue the issue of what's causing it.