My first service was done at 20,150 miles ( the computer said it had another 1000 before it needed it...) ....beginning to worry that this will have caused damage ...I did ring the dealer a month or two before to check and they kept saying it was totally fine and it was long life oil.
Your OK. The VW Warranty allows a certain "grace" period. If my memory serves me well, you are allowed upto 1000miles or 30 days, beyond the "due" date or miles (and yes, the ECU does keep a record of how overdue the service was carried out). Therefore, if you are on LongLife service, you could technically go up to 21,000 miles, or 25 months, from DoR/last service, and the warranty would still be honoured - don't take the p!$$ though!

Regarding the GTI being on the LongLife regime, enough as been said on this very thread regarding the "merits" and "de-merits". I'll get a headache if I keep bashing my head on the wall

Rgds