Avis deposit hold ****

I rented a car 5-9 December (Rental *** ) and a deposit hold was put on my cheque card for R3936.50 even though the Avis terms and conditions indicate that it would be not more than R2500 and weekend extra charges would be waved for Avis Preferred customers which I am (8MT76B). I have since requested my deposit back twice and was advised firstly that my invoice is still in 'billing' and then 'it been sent to management'. Avis terms and conditions also I dictated that lifting of the deposit hold can take upto 30 days, it has been 30 days since I collected the car and still my money has not been returned. I cannot help but suspect that Avis is collecting interest on all deposits it is holding for such a long time.