Customer service disappointment

I would like to express my disappointment and utmost frustration with the CSS group, I paid up my Capitec account in July that was handed over to them. I requested for a paid up letter a day after I had sent them the POP and they advised that they will send me a paid up letter within the period of 14 - 21 days, it’s a month later now and I am still chasing them to send me a paid up letter. Whenever I call to request to speak to the manager she is always not around or I get told that they will send an email to the manager to return my calls or respond to my emails , she never did.