2012 ARREARS DEMANDED IN 2015

So I wake up on a normal day and try to use my card that has a debit order on it that goes off every month..walla Its Warmed .I call African Bank and they tell me I have arrears of R1300 an something.something. I'm asking how that happened as my debit order goes off every month they tell me those arrears are from 2012 when I was unemployed and made a payment arrangement they kept on debiting my acc,Im asking why no one tried to collect that amount from me for 3 years .. NO answer..why was I able to use my card for that long and 3 years later its BLOCKED ,No answer...No one called me ..I have a debit order which I willingly setup myself when I got a job... the monthly installment was calculated for me by African bank that neglected to add arrears amount from previous years... even worse I was offered a credit limit last year but my account was in arrears..HOW ...WHY IS MY CARD BLOCKED IF NO ONE CALLED ME TO ASK IF THAT AMOUNT CAN BE ADDED TO MY INSTALLMENT...Y IS IT THAT FUNDS FROM 2012 GOT TO 2015????SOMEONE IS NOT DOING THEIR JOB AND I MUST SUFFER FOR THEM... UNBLOCK MY CARD!!!