Incorrect bureau posting

I app**** for data contract and they sent me airtime package of which I told them that is not what we agreed on. I did not even use it and was told it's canceled. Only for me to find out that they have listed me in bureau. I have asked them about this and have been told about 21 days what what and am sure that 21 days is way past and my details still appear on burea as a bad defaulting payer and that is defamation. I am sick and tired of this because I missed on proper accommodation as I was relocating because of mtn. They keep on asking me to contact legal department or legal will contact me and none of this has happened. I discovered this late Feb and made contact with them in March.