Sixt car rentals and first car rentals

Very bad service I hired a car from 1st car rentals for R2900, so they transferred my bookings to sixt car rentals since they were fully booked without telling me, then I went to sixt car rentals they said I must pay R2700 again the first R2900 was for paper work okay I paid. After that they said I must pay a deposit of R7000 which they promised to refund it back until today nothing.