Frustrated customer

I requested a paid up letter for my Personal Loan account, in July when I did a follow up i was told my account have a credit balance. I submitted a bank statement on the 6th of August for the credit balance to be refunded to me, I received my refund of R1539.23 and yesterday I called FNB for a paid up letter. Today I received an email stating that there is a credit balance again of R144, I don't know what to do I've been waiting for more than a month now for just a paid up letter. This is painful and holding my life back???can you please assist me and can this be finally over