Avis not refunding money owed to me

I have now contacted Avis on five separate occasions regarding the refund of my deposit, which is due back to me. My insurance company paid Avis in full for the agreed 30-day rental period. I also paid in full for the vehicle upgrade and insurance. As far as I am aware, there is therefore nothing outstanding on my account. Despite this, Avis subsequently deducted almost R1,000 from my bank account without my authorisation or consent. I have still not received a refund of my deposit, nor have I received a satisfactory explanation for the additional amount taken from my account. I have repeatedly requested that a manager contact me directly and provide a full, itemised breakdown of every charge, payment, deduction and refund relating to my rental. To date, this has not been properly addressed. I am extremely unhappy and frustrated with the way this matter has been handled. I have made every effort to resolve this directly with Avis, but after five attempts, I am still without a clear explanation or resolution. I now require this matter to be escalated to a manager immediately. I expect a complete written breakdown of my account and the immediate refund of any amounts that were incorrectly or unauthorisedly deducted, including my outstanding deposit. Please treat this as a formal complaint. I expect a prompt response and resolution rather than having to contact Avis repeatedly for the same issue. I am very disappointed as Avis is supposed to have great customer service.