Sprint sprint cellular services Rip Off charged for services I did not have or authorize Kansas City, Montana

I have been a customer of sprint for 20 years.  I have 3 phone active phone lines. Today i went in for an eligible upgrade on 3 lines. I was informed from the employee that i had been being charged on 4 lines for the last couple years. I had that line on my phone 4 years ago and had canceled it. The store employee said it was on my bill and was actively being charged. He was kind enough to get customer service on the phone. I explained to the gal that it was a line that had been canceled and i was overcharged for that whole time. She told me that they activated it a year ago and that someone must not have explained it to me very well . And stated i recieved some promotional credit and it was being charged again. I said why would pay and activate a line i have not had in years?? They went back to past bills and could see there was no activity on that line at all. I was in there to buy 3 new phones and she said she would credit 100.00 dollars. I was clearly upset that i was ripped off and she was telling me i authorized this and may not remember doing so. I would certainly rememeber activating a phone i had no used in years and canceled years before. Then she put a manager on the phone that told me i would recieve no money back at all. I was furious. I said she could cancel my 3 phones and she told me i would have to pay an early cancelation fee on this line that they added and i dont even have. This is bad. 20 years with them and this is how they treat me? So now I have to pay more money on a phone i dont have and canceled years ago. So it was inactive and they took it upon themselves to reactivate it and i never knew, Anything i can do ??? Now this will hurt my credit right .