unacceptable service

I have been trying to sort my account out for over 2 weeks with Cell C they are saying I have an outstanding balance however I have a email stating that I've got no outstanding amount when I canceled my contract. Every time I get asked to email the proof stating that I don't owe them anything when I email them the proof they don't get back to me then i send a email requesting feedback and they tell me that their team leader is handling the matter and that's where it ends. I really don't want to get my legal team involved in this matter. Please sort this out urgently