Unable to cancel Business Line

I have been trying to cancel a business DSL line since 23 Feb- to be stopped at the end of March. Surprise, surprise....several phone calls and several empty promises and still NOTHING! And every time I call in I have to go through the same process. The call centre consultants are really trying their best but the people you need to make the decisions are 'in the back office'- and nobody can contact them directly. I am so fed-up!