Reverse lamps are powered from the onboard control unit. You would have a fair few other things out also if this is the case.
Should be Fuse 17. Have you checked if there is power getting to the bulb side?
17 - Fuse 17 - 5 A
- Interior monitoring sensor -G273- 30a
- Alarm horn -H12-
- Dual tone horn relay -J4-
- Onboard supply control unit -J519-