Messed up billing

Rented a car from Avis on the 7th of August returned it on the 12th. Got charged twice and my bank account is on minus because of that been trying to sort the issue till to date. Apparently they can't even call their billing department they can only send emails so I must suffer while I'm not the one who created the whole mess. I will never use their services again and won't recommend it to anyone.