Vodacom refusal to send account closure letter

My contract was ended by the NCC in 2017 but Vodacom has kept my account open for a balance of R509 on my credit record, even though my cellphone numbers has been transferred to a new service provider. No matter what I do I cannot get a paid up letter stating that I no longer have accounts with Vodacom, once again affecting my credit record. I have called numerous times and always get put through to subscriber collections who state that I will receive a letter in 24 hours, but it never comes, I now spoke to someone with call reference number 005602 where she states that subscriber collections cannot assist with a letter an email needs to be sent to the relevant parties. Why do vodacom employees not know their own procedures affecting the consumer negatively once again. Seems the only way to get attention is to complain. I need that closure letter asap.