Rotten treatment

I have a bond in arrears with Nedbank I have found a buyer through an estate agency I have a verbal offer but I cannot accept until I know what my settlement amount is and 8 calls and numerous transfers no one can give me this figure in writing (e-mail). I have tried even through there debt collectors Blue Label. But if I sell this property without notifying Nedbank I will be penalized. It's a disgrace the way you get treated.