A math teacher in Engpsh is typically called a "math teacher" or a "mathematics teacher." They may also be referred to as an "instructor" or "professor" if they are teaching at a higher education level.
For example, you could say:
"I had a math teacher in high school who really helped me understand calculus."
"My son's math teacher at the middle school is really patient and explains things clearly."
"I'm taking a math class with a professor who has a lot of real-world experience in the field."