MTN is a ****

I'm beyond angry with MTN. I had a contract for 3 years which was closed about 2 months ago. To my surprise I woke up this morning with a debit order from MTN. When I called to inquire, the lady that was assisting me told me I don't have a contract anymore however is the insurance for the router that was opened by my sister which is a lie. How does my sister open a router insurance? she does not even have a router, how is it possible that she takes an insurance under my name on my personal banking details because the debit order went through my account. When I ask her to cancel it she says she cant cancel my sister must call to cancel. WHAT THE HELL??? WITH MY PERSONAL BANK ACCOUNT. MTN IS A ****.