Recommended rejection of a paper, but invited to review the paper again
This has happened to me a couple times. As Peter Jansson has pointed out, what probably happened is that, while you recommended rejection, reviewers 2 and 3 said "it's actually publishable if the authors solve such-and-such problems". This is the kind of situation where a sympathetic editor will make a "revise and resubmit" decision. 

In this particular case, you have it easy. Just write a very short review along the lines of "in my first review, I recommended rejection of this article because of [problem that made you recommend rejection]. As the authors have not addressed this problem, I'm regrettably forced to maintain my previous evaluation".

[FWIW, one of the times I reviewed a paper like this, the journal actually ended up publishing the paper in question, with the problematic section still exactly as it was  when I reviewed and rejected it. Go figure]