Test the fan with a 12 volt feed direct to the fan. If it runs then that rules out the fan
Assuming fan works then pull off the temp sensor connector and short two of the terminals together the fan should run now as the temp sensor will be telling the ecu that the engine is very hot (I have not had a need to do this on an A2 but this as worked on other cars over the years)
Should it still not work then the fan control unit is the next thing to try
Cheers