Multiple Monthly rental charge in a month

Hi, I have rented Hertz car for 8 months from Oct'17 to May'18 on the monthly billing. In the month of December i was billed on my credit card multiple times (3X monthly rental). When i bought this to Sandton hertz office notice, they were able to reverse 1 excess refund. I have submitted my credit card statements and have been following up since then. Two account managers have changed in the mean time and still no resolution. Please don't tell me to write to the customer care, I have done that multiple times. I have spoken to the customer service rep and was advised to visit the branch and send an email. Its been 6 months now and still this is not solved. The account Manager in Sandton Hertz also is fully aware of this case, she has my contact details.