Account fees

I am a pensioner and was informed by FNB that because of my age, I am not paying any account fees. Now all of a sudden this month, I was billed for account fees. When trying to determine why, I was informed that I must have an investment of at least R500000 with FNB in order not to pay account fees. First word I heard about this. FNB just changes the rules as they go along without informing the customers. It is time to move to another bank. My many years with FNB is coming to a close very soon.