Send it back to be re-made.
I can't honestly believe that people are advising anyone,especially a newbie, to dye the piece or hair?
No one should have to colour their own hair or the piece just to make it match.
And it should not be accepted as the norm either or some learning curve.
We send hair samples and also instructions as to what the hair colour should be, so it is hardly rocket science for the factory to match that.
The problem is the factories problem to resolve, and i am sure that John would agree with that?
As for the knots?then again if this was your only issue then bleaching them yourself is no big issue but as it is also coupled with the complete mismatch of your piece then send it back!
The black threads are sometimes white and sometimes coloured.(i know because i have had those before!!)
I was told by a factory once that they can be mistakingly left there by a new ventilator?
Unfortuanatly they have to learn and they practice with thread as it is easier for them when under tuition.
The other reason was that it could be a marker to let the ventilator know where he stopped the day before.