A company “accusing” someone of piracy isn’t proof. Access to the internet is almost essential these days. If you can prove a person is pirating prosecute them under the law with fines or even incarceration if warranted. But stripping internet access from someone shouldn’t be seen as an acceptable punishment for a free citizen anyway.
Whoever owns the network attached to the IP address also shouldn’t be responsible for actions of every user. Let’s ban an entire company, college, or government institution from the internet because an IP showed up on a list… dumb ruling.
That is not what the Budapest Memorandum says. It’s really short so you can just read it but it only requires the US to bring the matter to the UN security counsel which they have. Russia has violated most provisions but the US hasn’t violated any.