one month notice

I tried to cancel my account for several years now, but to no avail. the outlet I used was in Welkom and when I rocked up at the shop, there was a sign that said they had closed. No forwarding address or telephone number. I stopped the deduction at the bank, but they re-instated it again. Then I eventually got a contact number for mastercare on google and I phoned them. Cancelled my account on 28 May 2018, but end of June they again deducted the premium. I made enquiries and asked them about it, they said their billing month had already closed and that the contract said I must give a months notice. So I asked if my appliance broke within the notice month, will they repair it, and the answer is no. So my question, why must I give a months notice if I cannot use it.