If the issue is more specifically copyright infringement, then leverage the legal apparatus in place for that. Their lawyers might listen better.
This is not a strongly held opinion and if you disagree I would love to hear your constructive thoughts!
The best way to make sure your code isn’t copied is not to publish it.
I always found this weird while I was working at this company, but then, they have no reason to care about ephemeral threats that have never been brought to bear in a meaningful way. No consequences = no reason to spend literal billions retooling the entire tech side of your company over a decade.