My credits never replenish.

Yet again, my billing date has come around the corner and my credits were not automatically replenished. Last time I had to come on here and express my frustration until somebody replenished my credits manually, seems that it is the same situation this month. My billing date is on the 30th, so every month on the 30th I should be expecting credits to be refilled but it just simply doesn't. Can somebody please help me out and hopefully take some course of action to prevent this from happening again and again, from month to month? I shouldn't be on here begging for my credits to be replenished, especially after paying you guys the amounts that I have payed..