Scholarships for mathematics international students
Your best bet would simply be to apply and hopefully get accepted to a PhD program somewhere like the U.S or in Europe. PhD programs in math, or in STEM in general, almost always guarantee funding which is free tuition + research/teaching assistantships which give some salary. 

Once you are enrolled in a PhD program and impress in your 1st/2nd year, then a lot more opportunities open up ranging from grant funding from professors to prestigious scholarships from big companies like Facebook or Google . Note that these programs are extremely competitive like top 1% of top 1% PhD students are accepted. That's why I am encouraging you to get accepted at a PhD program first.

I am also an international graduate student and when I was applying to PhD programs in the U.S, virtually all programs in the top 75 range had guaranteed support in the form I mentioned above. Even Fulbright would be more competitive from what I heard from its recipients.