Unauthorised debit order

My name is Mandla, on the 19th of January I received a text message from Brooks and Luyt attorneys that reads, "Our client First National Bank is prepared to offer you a settlement discount on your FNB Smart account. Please contact Brooks and Luyt attorneys for details on this limited offer." Few days after receiving the message I called to enquire about the settlement amount and I was given a settlement of R1,950 and asked if I could split the amount into two consecutive months and they flatly refused. I then requested to call the office back towards month ending to confirm the settlement agreement and was advised to make payment within 14 to 15 days. On the 26/ 01 I called the call center to make agreement and also requested a letter of agreement and they promised to email the letter to my account on the same. Around 15-30 minutes later on I received a call from the call center informing me of the changes in our agreement, that I should now pay around R5,500 in three months, which I refused to make. To cut the story short, on the 27/01 a debit order of R4637.45 was paid from my bank account to FNB legal account. When I followed the transaction it traced back to collection from Brooks & Luyt. I wanted to close this account do away wit it Please help , I am so upset.

Mandla Vilakazi