I am in the middle of buying my new A4 and have a caravan so have done a bit of research on tow bars, I've found PF Jones are the best value and they do various styles, the westfalia one is identical to audi genuine ones at a fraction of the price.
https://www.pfjones.co.uk/tow-bars/audi-towbars/audi-a4-towbars/tow-bars-for-audi-a4-avant-estate/audi-a4-estate-b9-2015-onwards.html