Both are 'correct'. The first indicates the finished action; the second indicates the present condition.

Has completed or have completed Which is correct?

In my point of view, "I had completed my task" is correct, but for present tense it's become "I have completed my work" is correct. Highly active question.

Has been completed which tense?

Yes, they are both the present perfect tense. I would say that 'has been completed' is the passive [voice] and 'has completed' is the active [voice].