Money taken for overdue accounts which don’t exist

This company is taking off money from my electricity I purchase with a description arrears amount. From R500 they taking off R148. How can they claim an overdue amount if electricity is purchased from my bank account. I cannot get through to them and even after numerous mails no response. Please check your electricity units when purchasing. Luckily I looked at the mails I receive when I purchase and went back on previous mails where I picked up 2 x purchases with this problem. I noticed by the amount of units I usually get where the last purchase had 50 units short and that’s how I decided to actually go into the receipts sent via email only to realise what they doing. Something need to be done about this. They actually *****ing money blatantly for an account which they claim is overdue when we paying cash for the electricity. Disgusting Contour technology…I’m coming for you !!!