bad service on paid up letter

i have an account with ackermans that was handed over to DMC Debt Management . on the 20th november 2018 i requested a settlement letter from DMC Debt Management. it stated my settlement amount of R2175.72 that should be paid no later than 28 December 2018. On the 18 December 2018 i made a payment of R2175.80 on DMC Debt Management. Bank details as followed DMC Debt Management- account no ********** 07- Standard Bank-Ref ********** 3 settled. Today 14/01/2019 made a call to DMC Debt Management, spoke to one of the consultant that the account has been removed from them, they cannot not trace payment. i called ackermans spoke to Princess at collections department, she told that the account is no longer with DMC Debt Management its with another collectionms agency. she said i should email settlement letter and proof of payment to colections@tenacityinc that she will trace the payment. I need the paid up letter as soon as possible hence its almost a month made payment towards my account. Everyone is sending me pillar to post. before making any payments was receiving calls day and night. Soon after paymet there is no communication