Extending a contratc to 25 months

I have just upgraded my contract with tablet recently and decided to add additional line for my son Tablet both tables are for kids , but now Vodacom insisting to debit me twice which mean the contract will be 25 months not 24 months by debiting me twice on the same month . I don't understand why you're debiting me twice because if you have debited me after 48 hours receiving the product and debiting me on the debit order date the same month for normal debit order it means my contract is extended by one month literally. received a call from agent telling me that they received a call from senior level that they would cancell it and do it on two day before debit order, iam thinking cancelling both contracts and go nextdoor .