Charging interest after bond account was settled in full

We went to a branch to get a settlement figure for our bond account - they provided us with an amount that according to them, included the interest charged up to that date - they assured us that once we paid this amount in full we did not owe them anything - they confirmed that no more interest could be charged on this account as the balance was 0.00. I phoned the call center the day after we paid the full amount and they confirmed that our account was paid in full. Absa has since given our lawyers our house deeds as the account was paid in full (we have sold our house). Yet, on the 16th of February (after they have provided the lawyers with the deeds) - Absa deducted an amount of R1,504.71 off our bond account -(the description says - interest cap ) I phoned the call center to query this with them and was told that Absa is entitled to charge us interest, even if the account had a zero balance. The call center is useless they cannot help us - the regional office puts us through to the call center when we phone there for assistance - it is a viscous circle of incompetence and ignorance - everybody passing the buck and in the meantime I am losing money as Absa thinks they can deduct money off my account although I don't owe them anything .... I will not recommend Absa to anyone .........................