What should I do if I think that my former supervisor has published our results without citation or acknowledgment? A few years ago I worked in a lab as a visiting researcher (something like internship). As the result, I had to write a short report which at that moment didn't look like a proper paper. 
Recently I've discovered that my supervisor literally 3 months after my leave decided to present a conference paper with the results of, well, our work (at least I think that these two documents contain the same idea).

I do prefer to keep my old works and emails so that I can always check and find something. It seems that I sent a copy to my supervisor and the paper was submitted approximately one month later.

Since it's not so common, I've asked my former supervisor already and I've got a reply "What are you talking about?". Now I'm confused and feel a bit stupid because I might be wrong as well. 

I've checked related questions:
Is it plagiarism for my thesis advisor to publish a paper using content from my thesis without citation?
What should I do if my master&#39;s advisor used a figure from my thesis in a publication without citation or acknowledgment?
and I need to clarify my problem a bit. The idea of the project came from my supervisor, I was needed as a person to read a lot of papers and to do a lot of routine calculations (6 months(!)).

Is there anything I can do now? It's not like I care now about a conference paper, however, at that moment I was looking for a PhD position and all professors kept asking me about my publications and results of my internship. 
And I've sent that letter already.
People's work on a publication is attributed in two main ways: authorship and in the acknowledgement section. Here, you need to know if your contribution was significant enough for an authorship (it sounds like it wasn't), and whether your work actually appeared in these publications.  There are a number of resources and guides regarding authorship: one, for example here. The typical defining factor is making an intellectual contribution. The information you have provided suggests that you do not deserve an authorship, but probably should have been noted in the acknowledgements. 

In my opinion, this is not worth making a fuss over. In my experience, admission committees are unlikely to care about whether you appeared in this section or not. They care whether you were an author on a paper, and how your reference letters discuss you and your work. You will have the latter, as long you don't burn any bridges. In your discussions with potential advisors, demonstrate an understanding of why the project was important, and detail how you assisted the main researchers.

Citing your project write-up is unlikely to be appropriate - and plagiarism would probably only come into play if they copied and pasted your text without your permission.