Rain call centre harassment

Rain please stop with the harassment, I am now even annoyed to answer unknown because your people calls me day and night, I took a prepaid with Rain that comes with a free router but now I find myself being harrassed for R1749, that I have no idea from what because my understanding of a prepaid is a month to month service, it’s not a contract, if I did not make a payment than you cut off the services so my question stands, what the hell am I in arrears for, please make me understand.