IANAL, but if this happened to me I would be gathering as many examples as I could of this having happened to other people. The angle being: Google knows this is a huge issue. Effectively, they know that they have (presumably accidentally) created a really dangerous trap for small players, and have chosen to do nothing about it.
In some jurisdictions I think that reduces the legitimacy of their claim that you actually owe them money.
EDIT: Even better, focus on the examples where Google "forgave" the debt; you could argue that those examples prove that Google knows it's at least partly their fault.
In some jurisdictions I think that reduces the legitimacy of their claim that you actually owe them money.
EDIT: Even better, focus on the examples where Google "forgave" the debt; you could argue that those examples prove that Google knows it's at least partly their fault.