Bad Service

I called FNB Credit card facility because they debit my account a day earlier than my pay day, the gentlemen who helped me literally told me that I am lying when I say they debit me a day earlier and on top of that he tells me can not change it because according to his system they debit on the 15th. I mean it's my account that gets debited earlier and its been 4 months now with the same story, how can he tell me that m lying.