Thanks for the advise guys, I've got the sockets fixed 🙂
I was originally looking at the below fuse diagram, which directed me to the C7 fuse in the boot, but this wasn't correct for my car.
https://fuse-box.info/audi/audi-a6-c7-4g-2012-2018-fuses
the correct fuse diagram is below that shows 2 fuse for the sockets (B3&4 in the boot), which explains why the socket in the back was working when the others weren't
https://fuseandrelay.com/audi/a6-c7.html
I also located the fuse for the fuel flap lock (A8 in the boot) and its fine so I assume I need a new motor.
thanks again for the advise.