false balance on loan statement

Hi I have a loan with African Bank since 2015 June, in January 2019 as per loan statement my balance was R 851.03 of which I paid at the branch and the balance was R 0.00, Today I received a call from African Bank stating that there is R 30,000.00 outstanding and the agent wanted to know when I would be paying. this is very frustrating because to me it does not make any sense how can a statement be from R 0.00 to R 30,000.00? where did this amount come from ? why is the calculation so off? I need clarity please. this is totally unacceptable.