Billing for non usage

I am just going to keep it as simple as possible .About a year ago i was approached by Telkom sales people who came to my offices selling LTE for the house and i signed the papers allowing a debit order for R299-00 ,and they delivered the unit for me to install .After months( 6) of trying to get it to work and complaining they discovered we did not have coverage ,3 months later after the 6 months they sent someone to verify and confirm , no we dont have coverage . I have been trying on almost 12 months to cancel my contract ,but no luck ,and guess what they keep on debiting my account ,even after i instructed my bank to prevent their debit order from going through and i am not even using the service from day 1. i have been to their offices at the glen and they sent emails in this regard on my behalf but still the debit orders come off my account . I have numerous reference and case numbers from them and sent emails to relevant people ,but no joy . I am in future reversing their debit orders ,which i should have done long ago . Please can you assist in this matter .