OPEC is a cartel, they openly say this and determine production quotes. There is no law that will stop them from doing that.

OPEC is a consortium of nations. What law would they follow?

Countries in OPEC+ tend to not really care about little things like the rule of law.

What laws? USA or European laws have no effect on OPEC+ countries.

Maybe you should sue them at your local court. That'll show them!

Laws are enforced by violence. No violence, no law.

Don't like it? Don't buy their oil!