It is up your your wish to publish your research findings. That right does not belong to anyone else. As you are the first author of the manuscript, you would be the first to be blamed for anything misinterpreted or flawed in it. I'm not in favor of having your name in any other order other than the first either. If you are sure that you are not going to work with the same supervisor/ institution in future, you could actively oppose this act. Try to convince your forget advisor that you don't want this to be done. It would be also better to leave a note to the head of the respective department with respect to this regard. If he still persists and if you are aware of the conference to which the paper is submitted, send a formal mail to the conference committee about your refusal to submit your paper. I don't think your former advisor and his associates would try to publish your work again in future after you show how serious you are about not publishing it. This would risk damaging their reputation. If they try to publish it without your name and knowledge, then you could claim against them for act of plagiarism, noting the fact that your thesis is already published in your university.