Macy's

I've paid Macy's in full and ending with a zero balance before the due date-they have sent be a bill for $2.00 of interest! How could this be when my balance was paid in full? This is deceptive and I've noticed other folks with same complaints. Also, If you're like me, I assume there is no zero balance because I KNOW I paid it in full, so, I wouldn't expect another bill. If the $2.00 balance is not paid you will get hit with a $40.00 late charge. Do you see where this is going?