AVIS Cape Town/South Africa add a small amount onto my cc frequently. I rent a car from them at least once a month. Why do I stay with them? Because it’s better the devil you know. I now have an AVIS UK manager monitoring every aspect of my rentals. I pay the agreed contracted amount and not a penny more. I pay on Amex and go into dispute with AVIS via Amex and refuse to pay…never have.
Treat them as badly as they treat you!