Why is Avis holding my deposit for so long?

Really disappointing when a huge company like Avis holds your money as they claim for 7-12 working days. I cannot appreciate that in this era of electronic banking they have to wait 12 working days for a refund your deposit. In the meantime, I have that much less available on my credit card. Really not fair! I returned the vehicle on the 22nd January. I have not received an invoice from Avis or my refund.