I have a Audi A3 (8V) Yr. 04.2014 and at me the cable is functioning properly. Although some write that no sparks your A3 8V, for me it does what is namely to play music from a USB stick. I've also attached my iPhone to the sample, it was not recognized as an audio source, but it was charged :) what is not bad either.
Is Think about the software / firmware ... maybe helps an update from the manufacturer. My Software Version: MSTD_EU_AU_P3151