As title, I am still confused about the differences between certificates and diplomas.
Did you complete the full program of studies and exams in your country that are required to consider that you have fully completed secondary school? Then you have the equivalent of a US high school diploma.
Did you in addition complete the program of studies and exams that will qualify you to begin university studies in your country? Then you have almost cetainly completed a program that would qualify you for university-level studies in the US.
Ok, thank you! I am sure A-level would be equivalent to a US high school diploma then.