On a much smaller scale I did the same thing with a consulting contract. They sent it me and said to full in my own job description and "check the contract". The laziness annoyed me, so I altered the payment terms from 30 days to 7. Every month they paid after around 15 days and I let it go, but one month they hadn't paid after 31 days and I sent them an invoice for late payment for every single invoice to that date (only 4 or 5). I didn't think they'd pay it but they did

> Not content with winning his day in court, Mr Argarkov is now taking matters further and trying to sue Tinkoff Credit Systems for 24 million rubles (£470,000) over its failure to honour the contract he created. For its part, the bank is counter-suing Mr Argakov for alleged fraud.

> [..]

> The court is set to review Mr Argakov’s case next month.

Followup a few days later, they both withdrew their claims: https://www.themoscowtimes.com/2013/08/14/man-who-outwitted-...

Now this is a case that's something I can get behind and fight for.