Watch out on your credit file here - I had a similar issue years ago when I first got my AmEx and paid the bill manually forgetting that I had enrolled in direct debit during sign-up. I called up and they sent back the direct debit, but did it in a way that made it flag as a bounced payment so was showing up negatively on my credit file, and was causing issues a few months later when trying to move to Centurion as my payment history was showing as having a missed payment.