UNFAIR PRACTICE

So I have been banking with Standard bank for years, basically ever since I started working. I had a credit card with them and it was well paid until I lost/resigned from work because of personal reasons. 5 months after being unemployed I struggled to make regular payments. After I got another job, I made regular payments even though the account was handed over to the lawyers and I did mention to them that I am not working. When I got the new job, I made regular payments and within 5 months of that I had paid the credit card off.

I know that this affected my credit score. somehow. I now app**** for a Mortgage loan, and I got approved by another banks, but my own bank of which my salary goes into every month declined my application with the reason of "failed score" which my score was 803/999. Why should I continue banking with Standard bank then? So my own bank is failing me? I just do not understand how can I approved by other bank with that score but be failed by my own.