Someone cited citations I used without citing my work and effort in finding the references Recently I came across a conference paper that tried to solve the same problem I solved couple of years ago and published a workshop publication about, but using a different algorithm. In their introduction they mention and cite 6 applications that can benefit from the solution to this specific problem. Out of the 6 examples 4 are exactly the same in my publication word for word with 3 of them using the same exact citations I used. Which made me believe with zero doubt that the one of the conference paper authors read my workshop paper and found those applications and citations useful and decided to reuse them in their publication without giving my work proper citation for finding those references.

I have read through academia stack previous questions and all questions I found were researchers trying to figure out if citing the source without citing the middle resource was okay:


Attributing Second-order Citations
I have found theses on a similar subject to my own, and want to use
their references with my own text and a similar flow. Is this
plagiarism?
Citing a citation from a paper?
Is it okay to incorporate a block of citations from a review paper
into my own paper?
Is there a problem with citing the original source instead of the
source where the information was first found?
If I use most of the references from a thesis but not the exact
same sentences, is it plagiarism?


The consensus form the answers of these questions is that the middle resource should be also cited. 

Since in my case my work was not cited at all, I contacted the conference committee chair about this issue and showed that the citations I have used have been reused in the paper that was accept in his conference without citing my work. His response was "this related work discussion does not amount to plagiarism." and continued to say that if I am not satisfied with his conclusion that I can contact the journal and ask them for a full investigation of this issue.

So currently I am a little bit conflicted, is this a case of plagiarism? If so how can I proof that it is a clear case plagiarism to avoid a similar response from the journal editors.
No, this is not plagiarism, unless the authors specifically used the same wording as you. Citing the same sources as another paper is not plagiarism, otherwise anyone who cites an influential paper would be guilty of plagiarism unless they also cited the hundreds of other papers who also cited that influential paper.

In your specific case, you say 


  Out of the 6 examples 4 are exactly the same in my publication with 3
  of them using the same exact citations I used. Which made me believe
  with zero doubt that the one of the conference paper authors read my
  workshop paper and found those applications and citations useful and
  decided to reuse them in their publication without giving my work
  proper citation for finding those references.


This is speculation, and you can not know that this is indeed what happened. It is also quite likely that the authors did a literature review or simply knew parts of the literature, and found examples of applications that were relevant for their paper. Using the "exact same citations" is what is supposed to happen when you cite the same work.

Unless your paper is relevant and related to the work done in their paper, there is no reason for them to cite your paper, and citing work that is related to both your papers can not be considered plagiarism. At worst, you could argue that the authors should have included your paper in their related work.

Remember, people cite your papers for the work that you describe in that paper, not for the citations you give.