Discovery Bank charged interest TWICE even I settle my account in full each month by debit order!!

I have always settled my balance in full each month. Yet Discovery bank charged me interest on 19 April and 19 May. Call center staff says they are aware of the problem as it is happening to many customers so they are in the process of reverse the interest charges. But the tricky point is, THEY DO NOT KNOW WHEN THIS WILL TAKE PLACE (what kind of BS is that?)!! I will wait and see how this plays out before I decide on the final rating.