While the money they owed me was significant
it would have been difficult(and expensive) to sue google at that time. It would be very different today.I had to write it off.And they had the audacity to send me a 50$ voucher for adsense just after that...
That is certainly a challenge. It really irks me when there is such a power imbalance and people take advantage of it. When I have to use the courts, I generally use small claims court and represent myself when I can, and I've had good luck with that, even though the time and cost for legal filings is not insignificant. The amount they owed you was likely more than the max in your state for small claims, though.