Just found out my landlord has been illegal over charging me in rent what to do?

I live in a rent stabilization building in the Bronx N.Y, I went to DCHR(dept of community housing renewal) to file a lease complaint, in the process i found out that the old tenant of my apt was only paying 585.00 a month. i moved in 1 month after her my rent is 1,120 . i want to prove in court he has been over charging me but it takes over a year to 6 months for them (DCHR) to investigate it . what should i do . THANKS