Just got the car with no owners manual! Audi won't tell me they are probably after a service, Halfords was confusing offering multiply choices, they can't all be right. I read that on 2018 2 litre TFSI models different oils were specified and you could not move from one to the other, this might have a US website so maybe not relevant here? On all my other cars in the past I had a Haynes so knew what to do when or choose to have a garage perform the job, currently feel at the mercy of the main dealers who might be tempted to over service.  

Hello Ian,

Welcome, and thanks for joining. 
My recommendations are:-

Get yourself an owner’s handbook. You should find one on EBay. 
Can I take it you rang an Audi dealer rather than actually visiting their Parts Dept./ Advisor? 
I would be very surprised if they won’t sell you a litre of the correct oil - so for probably around £10 you will have the correct oil, so visiting will be the answer.
Alternatives:- 

Contact Opie Oils - armed with your registration number. 
Refer to the Castrol website - again with your reg. no. 
 

I would think the correct grade maybe 5w/30 to VAG spec. 504, but that’s my guess, and guessing obviously isn’t acceptable - hence your very sensible question. 
If my assumption turns out to be correct, I use Quantum Longlife  5w/30 - believed blended by Castrol, and was/is a VAG’s  recommended brand. 
Always available on EBay. 
I guess you will be using a quality German oil filter, and renewing the air filter at the same time, unless you have evidence of a recent change.
Perhaps you could let us know what you find Ian. 
Kind regards,

Gareth. 

Do check in case there is an indication on a sticker somewhere under the bonnet. Might not have one on an older car, but my new A6 this year had the correct oil specs clearly indicated. The manual then advised that you could top up with that spec at any time, but if the correct spec wasn't available it indicated an alternative that could be used only a limited number of times between each full oil service.

Thanks for the reply's guys I looked back at the paper service records from Audi and they just say " Changed Oil As Prescribed"

and no helpful stickers under the bonnet.

I'll try another dealer and and buy a litre as suggested; looked at e bay for owners manuals and pondered on whether they would be correct and complete for my car! Looked a second time a week later and all were gone, Audi wanted £42 for one but they were out of print and could not tell me when I would get it! Slowly getting to grips with the MMI by trial and error when parked.

Thanks again

Ian