Account randomly debited

I have a vehicle account with Absa that is in arrears. I have a monthly payment arrangement for it. I pay my monthly installments over the counter. I also have a savings account with Absa and what Absa does is that every time when there is money that is sitting in my account they would just randomly come and debit an amount and I already paid my amount as per arrangement. This has happened before, they investigated and refunded my account. This happened again last Friday. I had some money in my account which I need to travel on Friday and yesterday I noticed that Absa randomly debited R 3,200.00. I went to enquire at the bank this morning but the lady(who'se name I don't want to mention) on *** has not been answering the whole day. I need you to please look into this and credit the amount back into my account. otherwise whats the point of having a payment arrangement. Secondly, am I not allowed to have money just sitting in my account? Must I always fear that it will be randomly debited and then I must wait for days for a refund