That is a good question and I can understand your confusion. The play was originally written by Euripides and he certainly has the more famous play. In fact, in the ancient world, it was one of the great ones. It was written in 5th century Athens.
Seneca, who came 500 years later redid this play. This was not something uncommon, because the Romans often times redid Greek originals. If you consider the comedies of Rome, most of them are remakes of Greek originals. This does not imply that the Romans were copycats, but that the Greeks came first. Both play should be read, especially if you are working with Seneca. It might be helpful to compare and contrast.