If the authors did not change their paper in response to your review (which I assume you mean by "I was assigned the exact same paper"), then:
- Your review is still as relevant as it was when you first wrote and submitted it
- The authors wasted the time you spent reviewing
Here is another point to keep in mind, which reinforces point 1 above:
- You seem to be well-regarded in this community, since you got the same paper to review from two different conferences
In light of points 1 and 3 above, I would simply send in the exact same review you already submitted earlier. This way, you provide value at no cost to yourself.
In light of point 2 above, I personally would certainly call out the authors on this. Wasting your time by not even editing the paper in response to your comments is, in my opinion, contrary to the spirit of peer review and of the entire scientific publishing workflow. The authors should be made aware of this, and so should, in my opinion, be the Area Chair.
However, it is possible that your original review did not reach the authors - issues happen (although my subjective expectation is that it is far more likely they did get the review and simply decided to ignore it). So I would not cast my comments as "the authors wasted my time", but rather as "the authors seem not to have received my earlier review, which I am appending here, since it therefore is still as relevant as a while ago". Both the authors and the Area Chair will get the message.