A single sentence can contain one or two 了 le.
Verb + 了 le (= suffix)
The action is completed. I have stopped.
|I, me, my||study, learn||grammatical particle of time||three||year, surname||。|
|I have studied three years.|
Verb + 了 le (= suffix) + time + 了 le (= particle)
The action is completed but only concerning the three years. I am still studying.
|I, me, my||study, learn||grammatical particle of time||three||year, surname||grammatical particle of time||。|
|(Up to now,) I have studied three years.|