Fnb unprofessional conduct

Today I received sms : FNB, Dear valued client, a transactional hold has been placed on your account. Kindly contact *** or send an email to *** to submit your source of funds documents. Ref reducted FNB a div of FRB Ltd. Before I knew it my account was frozen. I was treated like a ***** whilst this is my own money. Why didn't fnb contact me first to obtain what ever information Before freezing my account. Very inconvenient nonsense. My account is still on hold meaning debit orders will bounce and limited funds to use in December.