I was charge 1 USD multiple times on Itunes Store

The following is my email sent to Itunes which is self-explanatory and their prompt reply.

I was charged USD1.00 twice because I hit the "DONE" button twice when registering my payment method. I hit the "DONE" button twice because it did not seem to work the first time. I tried the third time and hit "DONE" but it still does not seem like it was working but I was again charge USD1.00