AVIS customer service

Iv used their vehicle and returned it in time in the same condition I found it in but when it's their turn to return your deposit it will be follow up after follow up they don't even bother to call you back. They unprofessional as iv logged a query the day before and when I call I. Today they only process it today. Why must I make follow up with my airtime only to be sent from pillar to post. Very bad customer service