What are you hoping to achieve? If it’s to screw them for as much money as possible speak to a lawyer who can advise you on the best strategy for that.

If you want a small/reasonable amount of compensation and failing that, you want them to cease using your code, I would just talk to them. Put together what your licensing terms are and then simple case of pay or stop using. This the path I would recommend, and as long as the fee is reasonable, I (as someone who has to deal with this sort of thing in my current role) would simply pay, as it the normal cost of doing business.

The reality is that this is likely the fault of a nieve developer, not the deliberate action of the organisation. Aggressively threatening to sue etc is typically overkill and the sort of behaviour that causes legal teams then to restrict developers and prevent them sharing their code etc.