In Duplum rule not adhered to

Nimble Group is harrassing me every day with trying to force me into making a commitment to pay a debt. The Company seem to take over loan books that are outstanding and then call you daily to ask for payment. Each call they make adds admin charges of R23+ to ones account. Also they don't adhere to the Staturory law of South Africa regarding the In Duplum Rule, but stick to the common law In Duplum rule, meaning they can add interest as long as they want and as long as you are not paying. They accept any amount, but dont always tell you that this amount is insufficient to cover the interest on the outstanding amount. It is worse then having a bond, where you can at least see what portion of your payment goes to interest and what goes to capital