unfair collection

last year august/ October got a call to settle my credit card debt by paying an amount in 3 installments, Oct, Nov and Dec., which i agreed to, come the 25th October the debit order was unpaid due to financial constrains, Phoned the agency which Woolworth's hired to collect on their behalf, was told that the debit order can be reinstated and the payment will be Nov, Dec and January, which the debit order collected without any fuss, come January there was no paid up letter, when i called i was told that the account is still in areas. now i get a call from the different credit collector with me owing , i have the call which i placed to the place can i please get a settlement letter as i paid my due