Amending client's debit orders withput their concern

I am angry and frustrated by Cartrack's business procedures. I'm a permanent staff member of a bank and debit orders run on the 20th monthly. My problem with cartrack started in April on the 18th when it was a long weekend. They tried to debit the funds early and then changed my debit date to the 18th going forward. This has been happening ever since that they go into my account and try to debit on the 18th which is not my salary date. This month of June they ran they're debit order three times which has resulted to my current account being in a negative balance of R849.27 which reflects bad on my credit profile for future credit lending. I want to cancel my membership as this is highly unprofessional of them.