I did is the best international English choice.
I took does not tell us if you were successful or failed or left.
I attended does not tell us how many lectures, talks, seminars, classes, lessons, meetings or whatever that you attended.
I had an internship begs the question what happened to the internship? and why haven' you got one now?.
I did = usually completed, but you might not have done.
This is one of those occasions when a longer sentences is required, to clarify the situation.
For job applications etc go with.
I completed my internship at the X for the Y certificate whatever etc.
I completed my internship at the X to receive/be awarded the Y certificate whatever etc.