Charged double for over a year

When we set up our account after moving, the Xfinity rep made a mistake and set up two accounts for our address. We were then auto billed double for more than 18 months before we realized Comcast was listed twice each month. This ghost account was never connected to anything and we had no knowledge of its existence. Each time we call to get this resolved we are transferred around until they decide they need to work on it and call us back. The call back never comes and this has been going on for a year now. We were charged more than $3000 for an account we had no knowledge of and no way of accessing on the accounts website. Each time we call and spend hours on the phone with them they can easily see that this was their mistake, but no resolution is ever achieved.