Incorrect information used by FNB to discredit clients

I am a Private Client at FNB. I signed surety for my underaged son to buy a residential property as an investment in the early 2000's. The investment did not quite work out and FNB recommended he sells the property to settle the debt. In a badly suppressed property market he did not get enough to settle the outstanding debt. FNB then got him to sign an acknowledgement of debt on condition that there will be no extra interest charges and no fixed repayment terms either. My son signed the document and because he was older than 21 then, I can not remember whether I co-signed again. I bought a new car in 2015 financed by FNB (Wesbank) and in the same month a computer through FNB Smart Devices. The computer was payed off in June 2017 and I am still paying the installments on my car and this account has never been in arrears, in fact I am paying more than I should. Today I app**** to purchase another notebook through FNB Smart Devices and was told that I do not qualify for credit because of a poor credit record. This is absolutely not true according to my latest credit score enquiry. This problem surfaced some time ago when my previous private banker asked me if I don't want to settle my son's outstanding account to "clear" my credit record. I see this whole exercise as an attempt from FNB to get me to use my savings to settle an account for which they made and accepted the terms, earlier. I am sick of FNB and have already gave notice to close my accounts. I hope this serves as a warning for other elderly people to not get caught by such schemes by banks.