No, I'm afraid the total time you may work on the UK WHV is 12 months.
Participants in this scheme must not work for a period exceeding 12 months. This may be in one consecutive period or interspersed throughout the total stay.
http://www.immigration.govt.nz/opsmanual/34459.htm
I agree with RedVee that total time actually worked is what counts, and the IRD are not the final word on that. Calm down and get in touch with your old employer - just because you couldn't instantly do this doesn't mean he's vanished off the planet. (Or, didn't you send emails back to family or friends, or post on FB what you were doing back then? That might be a record of exactly what weeks you worked.) What you CANNOT afford is to breach the terms of your WHV when you're just trying to get a work visa. If you have to get a loan to support yourself if you find you need to stop working temporarily, that's a better option than breaking the law. But you won't sort out the options you have unless you stop panicking.