FNB NOT TO BE TRUSTED

I am disapointed with an FNB today when I check the balance on my credit card i found that they have reduced my credit limit facility without telling the reasons or even sms me why they have decided to reduce the credit limit. i want an answer why you have reduced limit without my knowledge. i i have never skip a payment on this credit card or any other accounts that i have or a default or I will have to close all the accounts that I have with FNB. i have checked the credit i do not have any default or arears on all of my account. I want an ANSWER.