Long overdue paid up letter

In May 2023, I started paying my discovery/ fnb credit card account through this company following a 3 months payment arrangement offer to pay off this account. My last payment was end of July 2023. After my last payment I did not receive my paid up letter. I thereafter started getting calls from the very same company requesting payments and I sent them proof of communication regarding the arrangement made to settle the account in three payments, and also submitted proof of payments, but the calls did not stop. I requested a paid up letter again and it has not been sent nor received by me. This year in September, I started receiving calls from a new company, DMC, requesting payments for this settled debt. I however cannot provide them with proof as I do not have the paid up letter. I have sent DMC the very same communication regarding the arrangement made with Hammond Pole Inc and the proof of the three payments made as the settlement amount. My credit information is deliberately misleading due to Hammond Pole Inc not honouring the agreement and arrangement made.