Has the garage looked at the spark plugs, coil packs, maf, camshaft sensors ect.
These links might help:
https://www.audi-sport.net/xf/threads/1-8-tfsi-error-code-p0304-misfire-p130a-cylinder-disabling.224701/
https://www.audi-sport.net/xf/threads/a3-1-4-tfsi-2013-cylinder-2-4-misfire-please-help.400579/