"have completed" v "had completed"

"For my communication skills, I believe I have very good communication skills because I have successfully completed several communication subjects which involved both written and oral communication three years ago. (added)".

 I would leave the second "have" out, it is not needed. (Called "cannibalism" by H.W. Fowler, - the swallowing up of one "have" by another).

For my communication skills, I believe I have very good communication skills because three years ago I successfully completed several communication subjects which involved both written and oral communication.

But I agree with Jim, it is a cumbersome sentence, using the word "communication" four times in one sentence is not very good communication!

I agree with the sentiment but not with your punctuation. (Ignoring the fact that you begin a sentence with "But")

Eimai, According to H.W. Fowler, Modern English Usage and the OED. it is an "outworn grammatical pedantry, a superstition, to believe that beginning a sentence with And or But is a solecism"  And I believe you once chided me for using an "archaic" word!

The punctuation was correct.  There was no need to use a colon after I agree with Jim, the next phrase, it is a cumbersome sentence, is not what I would call an appositive phrase or clause. If it HAD been, then you would have needed to use a capital letter following the colon. Likewise, there was no need to use a full stop after the word sentence.  I chose to use only ONE sentence. Also we do not generally put our replies in inverted commas. I use inverted commas, (or as the Americans call them quotation marks,) when I am quoting someone. Finally, (since people in glass houses should not throw stones,) you should have  known to place a full stop OUTSIDE the last parentheses of the reproduced sentence above.

Being away for 3 weeks, I am back on forum again. This is my 2 cents. I think different readers have different inputs, and one may prefer certain sentence structure over the other. To me, I would write it this way:

"I’ve  just recently graduated from the RMIT University with a  Master degree in  Professional Accounting where I had competed my studies on accounting and taxation.

"For my communication skills, I believe I have very good commands because I had successfully completed a few communication (courses) subjects with emphasis on both written and oral communication".

We don’t need to repeat “communication” in the above sentence. Doing so will sound redundant.  Also on a side note, completing a course does not equate to being successful in mastering that skill.