A3 8P New key coding.

Got a 2004 A3 8P 1.9 TDI which only came with one key so i bought a new key,had it cut and matched it to the central locking.
I send the ecu off to a company that can read the SKC and they send it back with a 5 digit code starting with a 5 and i now need to match it to the cars immobilizer.
However,from what i can find i need either a 4 (plus a 0 in front of it) or 7 digit code,have i been scammed or ?
If this 5 digit code is correct,can anyone direct me as to where to find a good guide to code it to the car ?
And should this code be a wrong one,is my car then scrap after trying or will the wrong code just prevent me from getting in to the coding process ?
The guy that will do the coding for me is using the latest updated VCDS if that means anything.
Thanks