worse service providers ever

i am so tired of this people. Worse service providers ever. I was contacted by a agent for a wi fi deal which i agreed to and then was told the speed was too slow. I then cancelled it immediately on the same day, 2 days later telkom called to confirm my cancellation. The line was never installed but now i continuously get calls from debt collection companies threatening to add me to the credit bureau. my credit rating is now being affecting and Telkom is not interested. Promised me a letter to show my account is up to date but have not received it as yet .I am tired and don't no what else to do. Went as far as cancelling all contracts with them and will advise everyone not to use they service ever again