Credit bureau update

I had a contract with CELL C which I settled in full but it still reflects on credit bureaus as an active account. I wrote to them regarding the matter but they still have not updated it. I don't know what else to do because experian required a paid up letter. When I give them the paid up letter, they said it's a statement not a paid up letter. I'm writing this review as an opportunity for them to update this on bureaus otherwise I'll have to take legal action.