debit orders

good day<br> <br> How can Vodacom debit my bank account for R1500 every month without me having a contact with them?<br> i mean, i dont even receive any airtime or data or nothing for that in return!!! <br> <br> 1500 x 10 months = R15 000!!!! i could have used this money to pay for a real contract or even better, BUY a laptop or phone.<br> <br>