Rip-Off : Charged twice for one service

In terms of my previous subscription (Smart M) I paid a monthly subscription fee of R280 - this subscription for November 2018 was paid, via debit order, at the end of November. On the 8th of November I renewed my subscription but moved to a Smart S+ contract at a monthly subscription of R260. I have just received my invoice for December 2018 (Smart S+) contract in terms of which I am charged an amount of R182 (8 - 30 November?) as well as R260 for December. This means that for the month of November 2018 I am charged R280 (paid end November 2018) + R182 (payable at the end of December) for a total charge of R280 + R182 = R462. How is it possible that I am charged two subscription fees for the same month - this is a total rip-off!!!!!!!!!!!!!!!!!!!!!!!!