Double charge on month to month fibre contract,BA***

I took a prepaid WiFi fibre with MTN in 2023 July iit month to month contract , as from September it was not working as I change the province due to work until a month ago where I received statement that's I owe R516.00 current & past invoice.i need to know how come on month to month service I am owing past month where no data had been used at all? My understanding I only receive service after payment can anyone explain this to me as I Only paid R270 today knowing my monthly bill is R249 Only i need to know the past invoice or arrears perhaps are for what?