Very bad customer service

This company thinks they are above the law,collecting on a account that was fully paid. I sent a paid up letter for my cell c account 3 months ago. And I was advised the case will be closed in 14 working days. It's been 3 months now. Every time I follow up with them they say, they are waiting for cell c. I don't know what to do anymore. This is still on my ITC profile