Avis not sticking to their promises, taking my money

Avis needs to get back to me as soon as possible because they debited my account but the car is still with me and now I received my salary and have no funds available due to them. I need someone to call me back as soon as possible because the bank can't help me with a dispute without any letter or any proof. Sent them an enquiry email on 17 April and still no reply. I need my money back ASAP