Cannot contact Dell Support

Hi, I bought a Dell U2718Q monitor at September 05, 2017 with 3 years warranty. Last year, I the monitor had display problem. Colors displayed incorrectly. Dell Vietnam fixed the problem. However, the problem happens again. I contacted Dell Vietnam. They asked me to provide images of the monitor without any reply. I kept sending them e-mail for weeks. But I do not get any feedback. I am really disappointed with Dell product, and Dell support.