Treating Customers Unfairly

I had a terrible experience with Telkom. I paid up my debt and I requested a paid up letter. Aget Lukhanyo said he had sent it which he never did and the agents there after were struggling with the system and refused to send me the letter or even proof that it was previously sent. I asked that my name be removed from the black list and they told me that they couldn't assist me or even transfer me to someone who could assist me. They kept struggling with their own systems making me wait for long periods. I then emailed the agent a few times, begging him to send me my paid up letter and he responded once to say he sent it on the 19th, which I never received it. This is not fair. All I am asking for is 1 paid up letter that I have rights to. Please remove my name from the black listing. I'm actually worried about starting the process of getting my change back as I slightly over paid. Will I even get it?