My supervisor published our work without informing us. Can we retract the paper from the conference in anyway? We (myself and my thesis partner) worked on a research problem in 2017 as part of our undergrad thesis course in our university under a supervisor. We successfully defended our thesis in our thesis defence in our university and prepared an IEEE-formatted paper as per the request of our supervisor as he told us that we would be publishing it in a flagship conference in the following year. I personally mailed the final version of the paper to our supervisor.
We followed up with him till July 2018 as the proposal had to be sent to that conference by July 2018. But our supervisor told us that he didn't want to publish it in that conference. He rather told us that we would publish it in a good journal in the immediate future. We tried to follow up with him on several occasions about that but he somehow skipped through the conversations.
At the start of this month, my partner was searching through some research work in IEEE where he saw a paper titled exactly to that of our thesis work. When he dug in, he found out that our supervisor published the paper in that same conference without our names. The conference was in October 2018 and the paper was published in IEEE Xplore in December 2018. We collected the paper and saw that it was the same paper with the same title that I emailed my supervisor (only a few words here and there have been changed, about 90-95% is the same).
He along with his name added his PhD supervisor (who is a dean of a renowned university in our country) and a Korean professor in that paper as authors. One similar case is here in which the victim was yet to confront his supervisor directly and also told later he was acknowledged at the end of the journal. But in our case, we didn't get any acknowledgment. Also when we confronted our supervisor with the matter, he told us that he forgot to include our names which sounded more like preplanned. He also told us to not raise the issue further and offered us to help to publish the paper by extending it in a journal in the future.
We have talked to the department head about this. Although he was hurt by it, he hinted that the department won't be able to help much as there were two renowned and influential professors involved. Because our department gets benefited from them in several ways.
We have worked so hard for this work for nearly one and a half years as well as spent some huge money to buy some equipment for collecting the dataset. We're totally distraught and shocked by this incident. We would like to remove that paper from that conference somehow as we've worked so hard for this.
Is it possible though? If it is then what are the procedures of retracting the paper from that IEEE conference? Or should we just accept our supervisor's offer and move on from it?
For your kind information, I have the email proof of sending the paper to my supervisor as well as our thesis book with our name in it as an acknowledgement that it is our work which was signed by our supervisor, department head, and an external professor during our undergrad defence.
Disclaimer: IANAL.

As you evidently realized yourself, your supervisor had no right to do that. It is a completely unethical kind of behaviour which breaches academic rules to a great extent.

First, you must carefully weigh your options. In particular if you and your partner are still in this department and plan to stay there doing your PhD for example, be aware that your actions might have serious consequences for the people in this department (especially the supervisor obviously, who would face disciplinary sanctions), and they might resent you for that; it could damage your chances there. 

If you decide to proceed, I would suggest to contact an appropriate instance at the level of your institution (not your department, since it proved useless). I'm not sure which one is the most relevant: I would probably start with a students representative or union, otherwise ethics board or legal office. I'm assuming that they would support you and in the end force the supervisor to retract the paper.

If this doesn't work for any reason, you can raise the issue directly with the editor. IEEE is likely to take this kind of issue very seriously, they will check your evidence and probably ask the supervisor for explanations. If they are convinced the paper will be retracted. In this case the consequences are probably worse for the reputation of the supervisor, the department and the institution: this a public sanction by a renowned editor, as opposed to the official author asking themselves to retract it.