Sounds like the problem is with the mechanic, not the car. Do you know what the code is? Maybe we can tell you something about it. Sometimes it is a common error to presume that the code tells you the exact part to replace. This is not the case. No car computer can do that (yet).
Given that the light was intermittent, my guess is that they repaired the wrong part, reset the light, pronounced it fixed, when in fact, it just came on again like it did the last 4 times.
Statistically, the Prius is one of the most trouble-free cars ever made in history.