1. Pay a lawyer or firm that specializes in this sort of thing to play whack a mole for you
2. Accept it as normal losses and ignore it.
Contrary to others claims here, it is not a 500/hour thing to do #1 when dealing with firms that specialize in this. it probably would be if you just hire a random one-off IP lawyer to try and deal with this particular instance.
Trying to deal with it yourself will be increasingly frustrating and time wasting for you. You will also never be able to prevent someone sufficiently motivated from doing stuff like this to your software.
Unless you want to spend your time dealing with those folks instead of building the software, you should hand this part off - it's not a good use of your time, value wise.
Put another way: most companies farm out processing of this sort of request to high volume low cost processing teams. Or AI. Or both. For you this is an important one off. For the person processing it it's one of a hundred tickets they are handling today. You are not going to get very personalized attention and consistency.
I don't claim this is how it should be, etc. I simply claim this is how it realistically is. It would practically require legislative change to have a different thing happen here and while interesting to discuss, that seems outside the scope of your questions, which seemed more practically oriented