please assist

Good day .I did a online application for a fnb credit card. it was declined on the basis that i do not pay my accounts on time, this cannot be correct ,I called fnb re this and was told that theres a code 3 or 33 which is why it was declined ,i was told that i owe fnb money and that there was debt which was written off. i can t remember that fnb has written debt off or that i still owe. if i had a bad credit history why would other banks approve credit and not my bank ? kindly inform me as to what the problem is