I've settled, why do you have to debit again

I called Vodacom in the middle of january or before the month ends after my Jan Debit order went through (20th). I asked in for a settlement amount. They gave me a form and told me to fax or email but they did not tell me when. I paid on the 30th and sent the cancellation on the 12th. On the 20th of Feb they debited my account again. It is not my fault that they do not communicate with each other. I called 082111, they said I should speak to the accounts Department ***. I called them then they said I should call the Cancellation departement as it was not their fault. I spoke to Khanyisile on ***, she said i should speak to the Accounts depart then I spoke to Mbalenhle then after that she said i should speak to the Contracts department, I spoke to Nondumiso at the contracts Depart, she said theres nothing they can do, I should go back to Accounts department. I am so tired of going up and down. Please refund my money. I took a laptop with Vodacom. I wasnt getting airtime or Data bundles, i was just paying for the laptop. I cannot be charged for just a piece of paper that is called an invoice. Communicate with each other and refund me