Why are complexes of type MA3B3 not optical active?

Complexes of type $\ce{MA3B3}$ have two geometrical isomers, namely:

1. fac-isomer
2. mer-isomer

If we look closely at the mer-isomer, it has a plane of symmetry, so it is optically inactive.But the fac-isomer has no plane of symmetry. Still, it is optically inactive, why?

Being a 12th grader, I wonder where am I wrong in my understanding of optical isomerism in coordination complexes.