Document it, get witnesses. That's harrassment. Do NOT respond or retaliate to them directly, it lowers you to their (pretty low) level. If possible, get a manager of the establishment involved, and insist on a neutral bi-lingual person with you for any confrontation or discussion.

Being a minority doesn't give someone the right to be racist, neither does being the majority. It's wrong, and people like that perpetuate the stereotype both within their circle of family and friends, and negatively with whomever they encounter.