The belt/chain situation confuses a lot of owners and not just independent but main dealers!! I would check that the two cam chain tensioners are being replaced with the new parts and even push for a new chain. There's a tensioner fitted at the bottom and top of the engine. It's normally the lower that fails due to oil pressure. There are auxiliary belts however they won't cause catastrophic damage as a cam chain tensioner failing... Once fixed the engine and car are fantastic. I'm glad I stuck with it as my car has a 2 yr warranty on the parts fitted and 4 yrs free servicing. How many 4 yr old Audis get that from a main dealer...?