What should I do if someone is claiming my research on ResearchGate?
I think the most important part of your question is the bit about "with the same name".  

ResearchGate has very loose and rather questionable practices in how they manage their citation data, which tends to err on the side of inclusion.  Moreover, their terrible user interface makes it very easy for somebody to do things like click "add all" and end up with a whole bunch of misattributed publications.  In the little bit that I played with ResearchGate before giving it up as basically useless, it kept offering to give me authorship of papers by people with the same last name---not even the same first name.  It will also automatically add papers to your profile in some circumstances.

What I'm driving at is that, given that you and this other researcher have the same name, it's plausible that they didn't even do this intentionally and have just written off the whole ResearchGate mess.  The fact that they didn't respond to your direct email is more problematic, but again not necessarily damning---you may well be going into their "headache pile" or even their spam folder.

Given all of this, what I would suggest is a two step solution:


If you think you have standing to do so, send a DMCA takedown notice to ResearchGate: it's fast, easy, and might get the content taken down.
After that, just start ignoring the whole mess.  It's not worth your time and energy.