Complain not attended

I am a telkom customer for about 03 years now every year on certain month they will not deduct installment come month end or during the month deduct installment plus interest i don't why last year January they did this this June monthend they did the same they didn't deduct on the fourth of July I saw the money still in my account I used their telkom app to pay but till today installment is not updated monthend July they deducted installment now when check on the it shows I am in arrears with R4643.92 how com I don't know this affect my credit I call them several times no one to resolve my problem and they continue to switch off and on services ****** tsotsi