i dont think you need to change the oil if the car has covered just 2000kms after the previous oil change.
You should have asked them not to change the oil if you did not wish to get it changed. The oil change intervals are pretty flexible even when your car is under warranty. Further more if you are not sure whether they changed the oil or not, then better look at it by yourself. Just open up the hood and have a look at the texture of the oil.
The A.S.S guys may say blah blah about the warranty void etc, so try to convince them by asking them to change it after a month. However if they dont agree you dont have any other option.