Still billing a cancelled contract

I have complained to Netstar about a tracker device that they have been billing me for over four years after I called them to cancel this.Their argument is that I did not follow correct procedure, in spite of the fact that they tell you that all calls are recorded for legal purposes (when I suites them). Taking money out of someones account without authority is an un ethical business practice. netstar appears to hide behind bureaucracy in defence of this practice. If I was a large corporate client of netstar they would take such a complaint more seriously, but I am a small entity and thus they don't mind treating me in this manner. I do not accept Mr Singhs defence of this practice and I would like to pursue this further.