Hi everyone,
I have finally solved the problem! Thank you Steve Q for the suggestion of an autoelectrician. I used Phil at Auto ETS in Watford who provided an excellent service!
I first got a problem diagnosis from him, which revealed the fault lay at the LED level, or the control module for it. I already tried changing the control module before and it wasn't that. The plan was to open the headlight unit and replace the LED and re-seal it. Turns out there are two further control modules inside which can only be accessed after taking the bumper and headlight out. One of them was faulty (Part no. 8R0 941 475B). They called Audi parts but it wasn't even listed on their system! Audi recommended that they purchase the whole light unit which would have cost me up to £1000. Fortunately, they tried VW and got the same part which is used in the Toureg. That part cost £400, pricey yes. But they fitted it and everything works perfectly again. Definitely saved me at least £700 and the stress of dealing with Audi Stealership + the lack of responses I got from the Watford branch (yes I'm talking about you Abbey, not even an apology when I complained).
I hope this info helps anybody else who has this same problem.