Need Help!!!! Refund due for Incorrectly Cancelling phone line

I have been  overcharged on a incorrect cell phone plan for a year or more now . I have spoke to someone about this about 3 weeks ago and it's still not been resolved!! My phone has been shut off twice already! And it's showing I owe money , when I am owed a refund . And I have been overcharged and owe nothing yet towards my current . I have asked for the refund to go back into the card on file. Which should be no problem since I'm the customer and I did not have any thing to do with this mistake . And have been paying my bill on time and it's my money !!! Please resolve this issue this is my life line .