FNB BUSINESS CREDIT CARD - ******** INTEREST CHARGES

I refer to our business credit card account, which we have been paying off at the rate of R500 per month. The in duplum rule is applicable on this account and no further interest amounts were levied. I have furthermore been informed that no further interest amounts would be levied. On 29/11/2020 you charged R344.53 interest and on 29/12/2020 double that amount, namely R689.16. I have called on the first occasion and was told I would be called back with clarity and I have called a second time both to FNB and Brooks & Luyt to get clarity as to why you are charging interest when I have distinctly been informed that no further interest would be charged on this account. I demand an answer, as this debit balance is now escalating to higher amounts. Please call me in order to resolve this matter. FNB has, without any notice to me, gone back on their word about no further interest being charged on this account. I demand an urgent call to clarify this.