The creak is standard bottom bracket creak, indicative of up-and-down play in your bottom bracket spindle. With cartridge bbs, you can get the creak both (a) when the bb itself is shot, and (b) if the adjustable cup isn't close enough to the cartridge. (B) can happen if either the adjustable cup or the fixed cup aren't tightened down fully. (Yes, the Miche track bb has two adjustable cups. But for this question, it's not so important.)

What you have, I believe, is (b). And the reason you can't tighten things down fully is:

You cross-threaded the Miche bottom bracket when you inserted it the first time.

This is why the threads in the bb shell are stripped; indeed, that's pretty much the only way to do it. Sorry, not Miche's fault, but your own (or whoever inserted the bottom bracket for you.)

Also, the lack of a lockring on Miche bbs is totally a red herring -- the cups will actually get tighter with the forward motion of the pedals. The bb came out some because it was never properly threaded in the first place.