unacceptable service and mischarges

SINCE OCTOBER WHEN MY 5 YEAR CONTRACT ENDED, I HAVE BEEN CALLING 3 TIMES A WEEK TO SORT OUT MY ACCOUNT. I GOT BILLED IN NOVEMBER AND WAS GIVING A ******* EXCUSE AS TO WHY AND WAS ASSURED IT WOULD NOT HAPPEN AGAIN.... I THEN GOT BILLED IN DECEMBER AND GOT GIVEN ANOTHER STORY... TAKE INTO ACCOUNT I CALLED 3 TIMES A WEEK WITH PROMISES FROM VARIOUS PEOPLE THAT THE ACCOUNTS DEPARTMENT WOULD GET BACK TO ME, THEY NEVER DID. I HAVE BEEN TOLD MY COMPANY IS OFF THE SYSTEM YET I JUST RECEIVED AN INVOICE FOR JANUARY. THEY CANT PUT ME THROUGH TO THE RELEVANT PEOPLE OR EVEN A MANAGER AND NO ONE EVER GETS BACK TO ME. I WANT A REFUND OF MY MONEY AS MY CONTRACT ENDED IN OCTOBER 2015. THIS IS UNACCEPTABLE!!!