Minor revision changed to major revision
In my field, biomedical science, it is highly unusual to hear back from a peer-reviewed journal within 2 days of resubmission. I would recommend double-checking whether the journal is a peer-reviewed journal and whether the papers published in this journal provide a significant contribution to your field. It is important to always check that as there are multiple predatory journals out there. As Roland said, you have two options. Certainly, you should always consult with your supervisor prior to any action.
Another point I would like to add is that usually when the reviewer finds issues regarding the quality of the manuscript, the reviewer will point out the specific issues in order to clarify where the authors have to work on before resubmission. It is very strange that you did not receive a detailed review.
As for the change from minor to major revision, that can happen. Particularly because not always the same reviewer will be available to review all versions of a manuscript, so in some cases, your manuscript may be sent out to a different reviewer after resubmission.