What does it say on the certificate, if it says accounting technicial diploma and if you are claiming points for that, i would put that down. But if you want it to be counted as a high school diploma, in your case, it sounds like you could put that down too.
In most countries, you have to do high school to enter university/college, etc. So if you are later claiming points for tertiary education, they might wonder how come you went to a tertiary institution with an accounting technician diploma, you could also explain it in a letter.
Anyway, it would be good if you provide more information, such as what it says on the certificate, whether you did some tertiary education after this diploma and are you wanting to count this diploma as diploma points under education points.