I suspect that the reason you lose students is because you are teaching with and American style. Although using fun methods seems great for the U.S. the families of your students probably expect a more traditional method. Its a cultural thing. Also the political situation between Mexico and the US isn't very kind at this time to the Mexican immigrant. They probably have difficulty seeing the value in the English language because job skills are more of an immediate goal. Unfortunately, sounds like you would do better going to a major city.