I have a master's degree in Mathematics in a specialty X. I got a scholarship to do a PhD thesis in a specialty Y in another country. I have started working on my thesis and I have devoted most of my time to read books and articles in order to get familiar with the speciality Y and with the subject of my thesis. My relationship with my advisor was very bad, he was not supportive and he wanted me to quit my thesis in first year, since he was convinced that I couldn't succeed it. Four years later, I have finished my thesis (I did the work that my advisor told me to do), However he has refused to approve it. Now, I have quit this thesis and I want to get another chance to do a PhD thesis in the speciality Y because I have worked so hard for four years and I have gained a good research experience (even though I don't have publications).
I want to contact some professors to ask them for PhD opportunities in their lab, but I don't know how should I talk about this (negative) experience so that I can convince them to work with me ?