Its not under NDA (both a non confidential activity and pre-exists the NDA which was signed for a very specific purpose). tldr they received a huge sale from my affiliate link, retrospectively changed the terms from a much higher tiered commission rate down to a flat %, then retrospectively changed the amount to be store credit, both of which breached their original agreement. The ~$50k is just what they admit to (but won't pay).
That's pretty scummy of them, 50k is surely worth involving lawyers.