If you don't want to utterly destroy your company's reputation and have every company that depends on Python or other critical open source infrastructure boycotting you, you need to stop. Just stop. Don't send out any DMCA notices at all, not unless you encounter a case of infringement so blatant that it is obvious to all. And then make the decision yourself, don't contract it out. The risk of damage to others and blowback to you is too great. You're risking the failure of your company if something like this happens another time after two high-profile cases; damage to your company could be that bad.

And here's the thing: if there's a match between the SymPy Docs and something you consider yours, the copying was quite likely in the reverse direction: the solution you claim copies something out of the SymPy documentation (which is legal, but it isn't yours).