SELLING ME A POLICY THAT I DID NOT ASK FOR!!!

Last week a lady called, I did not get her name ofcourse, regarding a MFC Motor Value Added product. I told her I don't want to pay anything additional. She assured me it was already included in my installment and she was just calling to inform me on the product. This morning I received a letter stating the amount of R112.79, and has added it to my monthly installment. Now when I cancel it, they say it will take 21 days and the debit order will still go off????? I DID NOT ASK FOR THIS! WHY SHOULD I PAY AN INSTALLMENT??