Private customer, but FNB failed me today!!!

I am currently a private customer for many years at FNB. You have to earn a minimum income to be a private customer. This morning I attempt to buy a very cheap Samsung A6 device of about R2500 on a contract and the transaction was declined. I have more than 3 times in my savings, my house is worth 1000 times this amount, my current account has more money in than this phone!!!! How on earth does this make sense?? I escalated this inside the banking app, without any success. I called the private banker, but she couldn't tell me why this happened. I am paying much more per month for this service, for nothing in return. The left hand doesn't know what the right hand is doing. FNB failed me dismally!!!!! I will buy it cash from another supplier, but I need the reason why it was declined, this is unacceptable.