centurylink phone service refuse to close account Nationwide

i have contacted them requesting that they close my account, they have told me that they were not allowed to close account.  i had to file complaint thru better business bureau repeatedly, demanding that they closed my account, then i called trying to reach higher level supervisor at the headquarter corporate office, they kept sending me wild goose and would not allow me speak with higher level supervisor.  i have done everything i can think of in order to get my account to be closed because i do not want to be their customer anymore after i have discovered that i have been paying bills while i have no service with them which mean they owe me more than 500 dollars.  i have called and they dismissed my complaint.  i even asked them to close my account, they denied my request.  i filed complaint like 5 time against them demanding that my account to be closed, they continued denied my request and still sending me the bills when i asked them to close account.  it seem that i am being hold as hostage by them to force me to keep paying monthly bills.  i dont want to be their customer anymore.  why they refuse to close account?   that is an rip-off!   the company is called " centurylink " and they are an telephone service that provide phone service, internet service, cable service.....   thank you.