PAID UP LETTER RUN AROUND AND CLUELESS CUSTOMER CARE

i have cancelled my contract and was told i owed nothing on the contract, but each time i call to request a paid up letter no one seems to know anything, i have called over 20times, a woman by the name of Palesa Nhlapo confirmed my cancellation but since 2020 April there has no reply to my emails and her calls go to voicemail, this is affect my Credit record and no one has the ***** to assist, i am so tired of calling and not getting assistance. CAN I PLEASE HAVE A PAID UP LETTER