Lendplus breached their contract which is against the law

I fell into arrears on my lendplus loan, which carried a total balance of R1,851.31. Because I was unable to pay the full amount immediately, I contacted Lendplus to negotiate a payment plan. Lendplus formally accepted a revised payment arrangement: I was to pay R150.00 in the 31st of August, and the remaining balance was to be settled at the end of September.I received a formal email confirmation from Lendplus approving this specific arrangement.Despite this legally binding, amended agreement, Lendplus bypassed our new arrangement and used the DebiCheck system to debit the entire outstanding amount of R1,851.31 from my bank account.When I contacted Lendplus to demand a refund of the difference (R1,701.31), they refused, claiming that I am bound by the original contract. This is a clear breach of our amended agreement, which was confirmed in writing via email. They had no legal right to debit the full amount after agreeing to the R150 structure.Remedy sought:I require Lendplus to immediately refund the excess amount of R1,701.31 to my bank account, in line with the payment arrangement they formally accepted.and i will also escalate to the NCR