Account Query

I am a holder of Woolworths Store Account. Previously my account was handed over to Anthony and Richard Associates (ARA) for collection. Initially I arranged a debit order with ARA to pay the money I owed Woolworths. Later I decided to settle my account of which they advised me to pay a total of R3748.00 of which I did on 2015-04-29. A month after I settled my account I received an instalment letter showing that I owe an amount of R450. I have since tried to contact their financial services and recoveries department to investigate where this balance comes from since I settled my account. They have since telling me that they don't know where it comes from and they are investigating, but in the meantime they don't stop intimidating me with sms's of collection. They have now handed me over to ARA again and possibly Credit Bureau. I don't owe Woolworths a cent and I need this matter to be resolved in order to clear my name from Credit Bureau. Tnx <br> <br> <br>