These questions are not answered by "Avvo Staff", but rather by independent attorneys as volunteers for business development or charitable purposes or entertainment. Generally the attorneys hope to interest you in hiring them.
As a new German company, you will likely want to hire an Internet lawyer with good international experience. That may be a large international law firm with offices in both US and Germany, provided they have experience and skill in Internet and copyright.
It is not surprising that a French ISP would not respond to a DMCA takedown request since the DMCA is a US law not a French law. You won't get much response in China or Russia either to a notice of violation of US law.
Some piracy you can stop, other piracy may be localized or in a "safe haven" jurisdiction that allows copyright infringement of this sort. You will need an attorney to assist you in resolving local infringement through foreign associate counsel. For you that will likely be best done through German law offices.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
You are describing what seems like it will be a major effort. I really think you need to identify an IP lawyer in the most appropriate market, which may be Germany or perhaps here in the US (or both) and form a strategy about how you want to handle these incidents of infringement. In some cases, there will be remedies and in others there will be literally nothing you can do.
I suggest that you consult with a lawyer in private and discuss your objectives in more detail. You can start by calling around to several for a free phone consultation, get some insights then pick the best fit to work with.
DISCLAIMER: this is not intended to be specific legal advice and should not be relied upon as such. No attorney-client relationship is formed with the law firm of Natoli-Lapin, LLC on the basis of this posting.
The question suggests that it is "your" music which is being downloaded, i.e., that you are the copyright owner. If so then you need to consult Intellectual Property attorneys within your jurisdiction for advice regarding your options.
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