Right now - fix those issues.
You can disagree with reviewers and offer counter-arguments at any time during the review process. There can be an irreconcilable difference of opinion, usually concerning stylistic choices; ultimately, it would be up to the editor and authors to resolve. But outright disagreeing from the very beginning is almost never a good idea.
You see, reviewers are not your enemies nor the obstacles standing between you and another line in your CV. They are fellow researchers who spend their unpaid time trying to help you improve the article and offering the perspective you do not have. They are among what is statistically likely to be very few people who will ever read this work, and they are generally more representative of the potential reader than you, the authors. If you fail to convince them, what makes you believe this paper of yours would be good at convincing anyone at all? And also, if the reviewer agreed with your main idea, would you be any more inclined to address these "minor" issues?
Try your best to understand the criticism and improve the manuscript. If you believe there is a conflict of interest or genuine stubbornness, claims along the lines of "the old result is flawless, the paper is wrong" are generally dismissible if the reviewer can not be bothered to elaborate on their stance. Of course, you should respond in a civil way, explaining that you have provided arguments A, B, and C, neither of which was challenged in any way.