Check engine light came on after exhaust repair on 2000 Nissan Altima

I had one part of the exhaust pipe replaced due to an exhaust leak, they said the second would have to be done in future, but right after the $600 repair the check engine light came on.
What do I do now, go back to same place? They said on phone it has nothing to do with what they did?

Asked by for the 2000 Nissan Altima
if the other leak is before the o2 sensor, then it may. have them check there work and pull the code. if you are not happy with them, then get a second opinion.