Take off $750 charge on account

I called your customer service department and they told me that I was on a $25 monthly unlimited plan then I get a bill stating I owe $750 charge for gigabytes. I was told I could only get half taken off but I would like the whole amount removed I wasn’t told anything about being charged extra gigabytes if that was the case I would of just stayed with metro pcs. Is there anyway I can get some assistance. Or can someone call me directly at [Edited: "Personal Information"]