Request to stop insurance on cell phone

On obtaining my new cell phone last year around July/August, I requested that my insurance be cancelled as my office had placed my phone on their insurance policy. I was told that the insurance has been cancelled. Since then every month I have been phoning and emailing asking why I am still being charged. I even logged a complaint MTN REQ:*** and they still just ignore me. I am feeling so frustrated I have just phoned them again and after ages of that terrible music playing in my ear I was cut off. I am feeling VERY angry.