Worst service from Avis!

I've been a customer of avis for quite some time. I've also purchased two of my vehicles from them and I haven't had any issues up until now. They double charged me for my vehicle and after a week of trying to get this sorted out they still haven't helped me. They keep on making false promises that the amount will be paid back, but this hasn't happened as of yet. Avis, this is ridiculous.