deposit not refunded and incorrect amount charged

I was incorrectly charged in my foreign credit card for a car I rented in August. When I received my statement I noticed my deposit had not been returned. I inquired with Avis and they stare they'd contact their bank to reverse the charge. Somehow they managed to cancel one of the charges and then charge me a different amount not equivalent to the bill received and I still don't know why or what happened to my deposit. Upon inquiring I've received a nonsensical email to which apparently it's my fault and I need to proceed with statements to Avis. Avis has not given me a break down of charges as I've requested, has over charged me, not returned my deposit, and not answered my emails. I'm disgusted. Basically my bank can't refund anything until Avis gives authorisation and avis is not replying or supplying info and basically said I have to get my bank to refund. So somehow it's my fault avis charged me completely incorrectly. I'd advise going with a different car rental