Account debited before salary date

My current account was debited for my last instalment to Capfin on Friday -17 April 2015 . My salary get paid into my account on Monday -20 April 2015 . The funds in my account was allocated for a purchase I was going to make on Saturday 18 April 2015 . when i contacted the call centre - they were not \interested "in the opposition that I was in - all they made reference to was its in the contract that I took . I was also told that even if I did not have any funds in my account - the debit order would have been returned and they would have then re-debited my account on Monday - 20 April 2015 . they did not show any concern when I stated that i would have been charged an Unpaid Fee of R 115.00 - if i did not have any funds in my account . thankfully this is the last instalment on my account - I would not use this company again - and after this experience - I would never recommend this company to anyone I know ."""