CANCELLATION OF DSTV SUBSCRIBTION FEE

Few years ago i bought a decoder from a furnisher shop (CANT REMEMBER THE SHOP) who arranged delivery and installation.Years later lightning hit the decoder ,i call DSTV who refered me to the nearest DSTV customer centre .On that day i was made aware that a certain sticker at the back of the decoder was been removed which tells them that someone tried to open the decoder.My argument was why will i try to open or fiddle with it if i had paid insurance all the years on it? Fine and well i accept and called in to cancel my installment cause i do not have a decoder anymore. Subscription fee was cancelled and when i was in the position to bought another decoder i called in to activate it again.Now i had find out that the insurance fee on the very first decoder was never cancelled and i am been paying insurance on a decoder that is not even working.When i called in i was told that it is my responsibility to call in and cancelled it myself.My response to them was is it not logic if you cancelled a installment due to a product that is not working,automatically the insurance also needs to be cancelled?Dstv refuses to acknowledge my claim by refunding the insurance money i paid on decoder all along as my second decoder which i bought second hand also packed up about four months ago.Is this fair to treat a loyal dstv customer client that never failed to pay each and every month like that?The current decoder i had now have no insurance and i was thinking the best they can do is to transfer that money over to the current decoder for insurance,before i start paying for the insurance again.Please advise is it right what DSTV is doing?