I have studied English in elementary school or I studied English in elementary school
So, should I say
I studied English at the elementary school, then high school and at the university OR should I say I have studied?
I think it should be in past simple since we know when it was, in the past, during my elementary school days and i am not an elementary school student anymore? and it's finished even though I still might be studying it (outside of these institutions), but I'm referring to a certain point in the past? Thanks in advance.

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Answer

Really 3 versions could be used, and to a native speaker all would be understood in context to mean 1 thing. The context ( your previous or following sentences) , more so than the tense you use, will determine what your real meaning is to a native speaker. But to be specific, simple past " studied" only if you are not studying English now. You can use 'had studied" because you are listing 3 instances taking place one after another, at different points in time. You can use "have studied" to be ambiguious about whether or not you are studying now.

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I think you should say "I have studied English.

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I studied or I have studied both say much the same.
You studied in the past.
I study 
You are studying now.
I intend to study
You will study in the future

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i have studied ....
because you cite 3 different moments in the past and at this moment you are exploring or studying the language here on italk