So sorry this isn't more straightforward for you! But I think you should feel good that the MaterniT21 test was negative. It sounds like ti was a good idea to get it done with 2 different companies. I wonder if they use different ways to collect the DNA. I think doing it again is probably a good idea to be sure.
The nuchal measurement is not conclusive on its own because I think only about 60-70% of the down's babies have an abnormal nuchal. So it's good that its normal but not conclusive. But that test only gives you odds in any case so it's not positive in the sense that you had a positive test, but rather positive that you are in the high risk category. But you were already in that category based on age alone so it's really not that different.
You can also get an early amino at 14-15 weeks, I had one done when our nuchal results were 1:7 for a previous pregnancy. We got the FISH results back in less than a week. I can tell you more about that if you are thinking about it.
Try not to stress, I think having those Materni21 results should be really reassuring. I think the docs etc are just freaked out by it because it is new.