Considering that the Odometer is is linked directly to the ECU and the twits had to connect to the ECU, a) they did it. b) they may have had a computor glitch or power surge which has caused it with out them know or not wanting to fess up as the cure is probally a New ECU.
Does the Odometer still work, does everything else still work properly, dont let them fob you off. do you have a "deptartment of fair trading" (run by Gov) over there, here if someone tries to fob you off you only have to mention the name dept of fair trade and they usally backpedal real quick
maybe run it by your National Triumph Warranty Manager, there should be bone at Triumph USA, I know you are going to say it is out of warranty but the dealer still has to answer to them and warrant any work he does, that is why is a Triumph dealer because he is supposed to only have techinians who are qualified to work on and are supposed to keep up to date with everything Triumph relatted