If the domain owners are not cooperating or irresponsive, you can escalate things and contact the hosting provider. Please allow some time for domain owners to respond, but 1-2 weeks usually is enough and you can proceed with the next step. ISP (hosting provider) is usually required by legal regulations to comply with Intellectual Property law and are obliged to remove the infringing material, if you can prove ownership.
The success rate of this step depends a lot on the origin country of the hosting provider. If the ISP is from USA or Europe, it is very likely that they will take action and do as you ask. If the ISP is from Russia, China or other countries which do not oblige to Western standards of IP rights, the success rate might be much lower, but it is still worth trying, as some of the ISPs are accepting the requests and taking action.
How to find ISP (hosting provider) contacts?
Check on WHOIS database and look for “Service provider” or similar contact details, which would indicate the hosting company, responsible for hosting the content of the website. Quite often the email address for such reports will have a word “abuse” in it, as it is intended specifically for copyright, trademark and other abuse cases. You can use this email to contact the representatives of a hosting provider.
The recommended message for hosting provider
Copyright infringement notice
I am providing you this letter of notification to make you aware of material on your network or system that infringes the Intellectual Property rights. This notice is addressed to you as the agent designated to receive notifications of claimed infringement. Under penalty of perjury, I hereby affirm that the undersigned is the owner of IP rights to the copyrighted material that is infringed as described below.
I have a good faith belief that the link found at the following address http://example.example infringes my IP rights (copyright) to the 3D assets. I am the author of this content and the material was published without my consent and knowledge, thus infringing my Intellectual Property rights.
You can see my original work as an evidence on the following link:
I have contacted domain owners/admins requesting to remove the infringing content, however they did not comply with my request.
Based upon information at disposal, I believe that the statements in this notice are accurate and correctly describe the infringing nature and status of the Infringing Material.
I am hereby requesting you to immediately remove or disable access to the Infringing Material at the following link http://example.example.
If this information is not removed after notice, the Internet Service Provider may also be held liable for the copyright infringement.
Should you have any questions, please contact me by replying to this email.
(First name, last name)