If "they" (assuming this is shoreside) told you that you had it, and then not . . . sounds like politics might be in the mix. Do you get along with onboard management /have good evaluations and recommendations from them? Or maybe someone with more seniority or stronger qualifications got the job instead? If you were doing the job already, it's worth documenting or logging what you're doing and having a supervisor sign off on it. I don't know how NCL works these days so can't say for sure if on or off the ship is the best to approach the situation.
On my line we actually do have a 'promotion' form specifically for light techs. Has about 20 items that the production manager and cruise director have to sign off on. That, with a resume and a log of individual activities (repairs/maintenance/shows done) gets sent to the shoreside technical/scheduler folks and then the interview and placement goes from there. This happens either on or off contract. This is why I think it's better to get things done while you're onboard, as it's REALLY hard to get people onboard to help or respond once YOU are off the ship. Trust me on that one!