As above, your 2004 A3 2.0 FSi non turbo has both a timing belt and a timing chain.
Belt from Crankshaft - waterpump - camshaft
and
Chain from exhaust cam to inlet cam.
Only the belt is a service item that should be changed at a set interval (60-75,000miles (depends on who you ask) or 5 years). The chain only needs changing if you are experiencing problems with it.