My mnger and cowrker discss bad thngs abt me in frnt of me and thnk i am stupid, doesn't undrstand wht thy say

They think I am stupid, my manager think i have a comprehension problem. I m here in this country for 4 years and speak fluent english. Although i get nervous when my manager is around and bound to make 1 or 2 mistakes. Please help me to get rid of this nervousness.