Deposit still on paid

On the 25thmay i hired a car at avis in Cape Town airport, i returned the car on the 1st of June, however on the same day i asked them if they can extend the contract for few days but i then asked them to cancel the booking within a space of 30min so they said they won't charge me anything, i was then waiting for my deposit money since from 1st of June till today i went to avis to enquire about my deposit on the 30th of June they said i must wait for 2 days and i went again using my own fuel from brackenfell to the airport 3 days later still nothing they made me to complete a form and they confirmed I will receive my money after 2days, we called Nedbank several times while i was at avis they couldn't locate the money and we called my bank still we couldn't get any assistance. All the consultants I've dealt with at avis no one seems to help all they say it has nothing to do with them but it's my bank FNB how so? Cause i hired a car with them not with fnb no one took an initiative to go an extra mile to even contact me after those 2days asking if my money is back to my account i have to again drive to the airport myself where no one will even care to assist me. I need my deposit ASAP