African Bank capitalizing on loans

Good afternoon I have two lending accounts with African Bank. One is a loan and the other a credit card. I've never missed a payment. However, approximately 2/3 years ago, I requested my installments to be made less per month over a longer lending period. I was told that due to the new legislation that option was not possible indefinitely. They offered it for three months and the initial lending amount would resume directly thereafter. My date for debit orders are the same day as my salary date and I used this mode as confirmation that the debit orders were going off each month. Almost a year later I was being harrassed daily as African Bank did not automatically resume the initial agreement amount. I am now listed with a bad cedit record because I am In arears through no fault of my own. African Bank has sent me two letters acknowledging their mistake but I dont think I should be paying the arrears because it wasnt due to no payment. Now its interest as well. Please advise and please assist me. I'm struggling to even obtain wifi for my son who commences high school in 2020. My credit record is important to me. Kaashifah Jacobs