MTN takes my overdraft money for a product that I cancelled same day without using it.

MTN takes my money for a product that I cancelled same day without using it. Lulu Liu sold me a contract and when she didn't want me to serve notice with my current supplier to avoid overlap. So I told Lulu to cancel the whole contract and take away her MTN modem and sim. Lulu and her MTN didn't invoice me on the first month, second month they deducted R1565.13 in October 2019 and they want more in November 2019 as they just sent an invoice. I am stuck paying interest for overdraft for something i do not have and never wanted.