If you have an 8mm spanner, you can fix this yourself. Take the EXT box off (thumbscrew), see a brass nut, put the spanner on it and test which way it will turn (it turns only one way), turn it the other way 13 clicks if you want to count but in any event until it won't turn any more. In neither instance force anything. Put the EXT box back on; you may need to wriggle the rotating handlebar control the tiniest fraction. You should now have 14 gears, i.e. 13 clicks.
If you don't have an 8mm spanner, check where the handlebar rotary control stands, either 1 or 14. Take off the EXT box by undoing its thumbscrew and pulling outwards. Let the EXT box hang. Rotate the rotary control at the handlebar all the way to the other end. Put the EXT box back on -- you may have to wriggle the handlebar control the tiniest fraction -- and do the thumbscrew up again. You should now have 14 gears, i.e. 13 clicks.
