Settlement of Woolworths account in May 2016 already and still being harrassed due to their staff not doing what was expected when I wanted to finalize the outstanding account

During the month of May 2016 I contacted MBD to enquire on a settlement amount for my Woolworths account. the agent that assisted gave the amount but informed me that settlement can only take place via debit order in which I had to provide my bank details. The arrangement was that the debit order has to go through on or after 15 May 2016. I kept on viewing my bank account awaiting the debit order to go off. On 28 May 2016 when nothing happened I paid the settlement amount in full via EFT. To date they do not want to commit that they did wrong and are still harassing me for outstanding money however everything has been paid. I feel like I am being targeted for additional monies which I definitely do not owe.