JET installments that we not getting balance of the money that we owe

I am writing this on behalf of my mother. She had a JET account since 90s. The problem is this, it's been long she was not talking anything at JET, she was just paying for more than 2 years now. The time when she was using it she never owes more than R5000. Since she was just paying. I go with her jet to check the balance and they said she must do it on line. She try calling but they said she must do it online. I try for her it gives message with the number to call but they told me I am not allowed to do it for her. When she calls, they keep saying do it on line and online it gives you the number to call. So I dont now she will pay until when because they keep sending message for payment. Her name is Mushathama Helen Tshiambwa. ID no ***. Phone number is ***