International Math conference rejected paper without any comments!
Remember that for any journal or conference, it is ultimately the editors (or organizers, program committee, etc) who decide whether to accept a paper.  The editors assign reviewers to help them make that decision.  But if the editor is already convinced that the paper will not be acceptable for publication, then they may reject it without sending it to a reviewer.  This is called a "desk reject".  In such a case, it can happen that no further comments are given, or only vague comments such as "not of sufficient interest".

This is certainly frustrating because you get no indication as to how to improve your paper.  But keep in mind, ultimately it is your job to write a good paper, and it is not the job of editors or reviewers to help you do that.

About all you can do is to reread the paper afresh, address any shortcomings that you find (or already knew about), and submit it somewhere else.