Pathetic service and support!!! ********ly debited no reversal

I am extremely frustrated with FinChoice, they incorrectly debited my account with an amount of R 12 000 rand on the 24th of April - this after MULTIPLE calls to the contact center in March requesting settlement letters for my accounts with the company - this was provided and i paid both amounts on the settlement letter in FULL assuming that my accounts were settled i then requested a paid up letter for my accounts and was told no i still have an amount of R 1200 +/- owing on one of the accounts - which was discussed would be debited in April - they then debit my account for 12K !!!!!!!! I have been in contact with their contact center everyday requesting this error to be resolved and nobody helps - i get a different story from each consultant - no managers are available to speak to and nobody EVER calls back. I am furious as this is a large amount of money !!!!