if you are unsure then get it serviced, or change the parts yourself and keep the receipts. use genuine parts as they as just as cheap from the VW Trade parts. Better to change the oil than wonder if it has been in there for too many miles and be running on crappy oil doing more damage than good in the long run causing you a bigger bill.
If you are unsure about the service light just ignore it and go by mileage, every 10,000 id go for and even a oil change inbetween that for the sake of £ 25-30 for genuine oil+filter