Proof of Payment not going through Cellc due to incorrect email address given.

I have an issue with Cellc. All along I thought that my niece's cellphone had been paid off, until she called me a said MBD is threatening her saying they were asked to harras her by Cellc. I called Cellc and the lady that went through the account said there is still R186.00 outstanding. I asked them why was she send to MBD instead of them calling Cellc direct, they did not give me an answer instead they went through her account and then came up with the last outstanding figure of R186.00. I paid it immediately and asked them to stop the harassment. I then send proof of payment to Cellc, they came back and said even though they have received it I must then send the proof to another email which is ( proof of ***) so that the matter can be resolved quickly, I did that but that email address keeps on rejecting saying there is no such email. What should we do now, can Cellc please advise. My niece is being harrased by MBD and when payment is made Cellc gives us wrong email addresses. The cellphone number in question is ***.