Store sold me a false BOGO

I was sold 2 phones that were advertised as bogo and was told my bill would be high for a few cycles but then would go down to reflect the bogo... it never decreased.  I went back to the store and they have since closed... visited a Corp store and was informed that the particular phone had never been on this promotion and that yes indeed I am being charged for 2 total phones.

how do I go about getting this resolved.  I would never have bought these phones if they were not bogo.   I was clearly lied to and taken advantage of and would like to have a resolution.