Trying to cancel insurance

I downgraded my contract and cancelled my insurance end of 2018 in a vodacom store. I was assured that it was cancelled. Still up to this date, they keep charging me for insurance after In the meantime I have sent numerous emails (some of which returned), called in and transferred from person to person and every time they assure me that it has been cancelled. I have asked to be refunded for all the months since I initially cancelled as well, but as it might be imagined, have not heard/received anything back. I am at a point where I do not know what to do anymore as it has almost been a year now that I have been paying insurance on an Iphone that is not even being used.