i got this car in feb and about after 2 weeks the engine managment light come on i had 2 hub sensors replaced and new electric system replaced, now my engine managment light keeps flashing again i konw it needs a service not sure if thats why and also my exhuast seems to be a bit blowy, if anyone can shead some light i would be very gratfull,thanks

you'd be surprised if you saw this cars review, did u even test drive the car? or compare it to others?

http://www.parkers.co.uk/cars/reviews/audi/a2-2000.aspx

I would start by getting the exhaust sorted first as this may very well be why the engine man light is coming on.
The service reset is as follows.
A=R/H button B=Left
Press and hold button [A]
Switch ignition ON.
The words "SERVICE" or "SERVICE IN xxxx MI" will appear in the trip recorder display.
Release button [A].
Press button [B] to reset the display.
The words "SERVICE IN 10 000 MI" will appear in the trip recorder display.
Switch ignition OFF.
Good luck.

As you said that hardly two weeks went of your new car so its better to check with the car show room dealer.He will solve the problem.Don't worry.