Worst customer service and zero follow-up

I have an RCS credit which I have been servicing accordingly to the agreement. The call center called me countless times to make the necessary payment arrangements which I did follow through. It has now been 3 months of multiple emails and calls from my side requesting a letter stating that my account is settled. I received a call from a consultant who insisted that the said letter was emailed to me in December, whilst on the call with her I checked my email/trash and spam and cofirmed that I have not received it. I requested that the email be forwarded while we were on the call...10 days later I am still waiting.