Telkom and Nu Debt false claim

Telkom and Nu Debt have been threatening to blacklist me for an unpaid account. I have requested them to send proof of what I owe them but both are failing to do so. All they say is I might have missed some payment, they cannot tell me which month and a year. All I need is proof of what they claim then I can make arrangements to pay. I cannot pay for something I do not know just because these 2 bullies say so.