Very disappointed client

So I app**** for vehicle finance over two weeks ago, other banks approved me, but Wesbank did not, I asked Wesbank on the 2nd of Feb on Twitter after I tried calling their customer service multiple of times, why I would be declined they promised someone will get hold of me before close of business THAT DAY, eventually someone got hold of me the 4th of Feb we chatted and I explained the situation, she said sorry not her department someone will call me back just now, today is the 11th and still nobody has picked up a phone, but through the dealership i found out its because the bank I had financed my previous vehicle indicated I missed 8 installments, i pleaded and explained this situation with the customer service on twitter they just refused to assist me or give me a call to say what i can do next, I asked the other bank to sort out my profile as i was late on one payment, not missed 8 as the other bank indicated on my credit profile, they eventually sent a notification out to the credit bureaus to correct my profile, I saw on Experian it has been corrected and my score is above average now, I phoned the dealer to send the application in again and again it has been declined.

I have been banking with Fnb over 10 years. I have had two other vehicle loans from Wesbank I paid off two years plus in advance My personal loan is basically paid off in half of the time, my credit card is on date Why would other banks approve me but not my own?