Credit card

I am not sure why this is happening, however it seems that Standard Bank cannot resolve the matter. On a continuous basis I am receiving the same SMS and letters indicating that I am defaulting on my credit card payments. Every time I phone Standard Bank and very time they apologies, what happens ... another SMS or letter pops up! Firstly, my payments were done via debit order, according to Standard Bank I still defaulted; secondly I made a final payment on 15th of January, the account was closed, even received a letter confirming closure, I receive a letter dated 21 January indicating that legal action will be taken if I do not settle my account immediately because I continuously defaulted, really ..... My question to Standard Bank is, what is wrong with your data on your system and why cannot anybody fix this? Why is it so difficult?