FNB unprofessional and treats law abiding clients like *********. No follow up support.

I have been with FNB since approximately 1977 and for the first time I am livid with them. I received a denigrating and highly unprofessional SMS from FNB: FNB, DEAR VALUED CLIENT, A TRANSACTIONAL HOLD WILL BE PLACED ON YOUR ACCOUNT DUE TO OUTSTANDING DOCUMENTS. KINDLY CONTACT *** TO SUBMIT YOUR?ffffa0 SOURCE OF FUNDS DOCUMENTS. REF (....) FNB a div of FRB Ltd. All I did was sell some shares and use the money and they assume one is a ********. I have been on the phone twice with FNB to try and sort this out. They promise that I will be contacted so that I can send in supporting documents, but nothing happens except that the above threatening SMS gets sent again. I made it clear on the phone that this whole ordeal is causing me huge stress but sorting it out seems to be of no priority at all. The FNB site has also been of no help in determining where such documentation should be sent. The SMS is so unprofessional that it really looks like spam, but it isn't - All CAPS with a parameter?ffffa0 which hasn't been substituted properly.