Still awaiting paid up letter many years later

On 16/09/2019 I settled my cellphone contract account *** with cell c with a settlement amount of R961.94. I have been requesting the settlement amount ever since and never got it. Every time I follow up I am told the case has been closed. I recently spoke to Nokulunga call ref *** and was promised I will receive it and I have not. I am very frustrated for a customer that has patronised the brand I am very disappointed. Al,l I am requesting is a paid up letter which I am still awaiting many years later