Incorrect billing/debt

The last time I used my Rain Simcard was in July of 2021, and as far as I know Rain provides a month to month service meaning if I don't pay I don't receive their service/data. Now I am being told I owe R1,437.00, which does not make sense. I have not used any data from RAIN on any of the dates they rea billing me for, and how do I even accumulate such a debt on a month to month contract.