Same issue happened to me, Google responded several hours later with the following email:
"""
Dear AdMob Developer,
Last week, we wrote to let you know that on December 19th 2013 we would initiate refunds to you for unused legacy AdMob advertising credits. Today we are writing to let know that between December 19th and 20th we inadvertently processed refunds for more than your unused balance. In some cases, customers will see multiple refund amounts on their bank card statement.
To correct this error, we have reversed these incorrect refunds with corresponding transactions for the same amount(s). These corrections have been processed on December 23rd and December 24th to the same bank card that the initial refund(s) was processed to. This means that you will see one negative and one positive transaction on your card statement for each refund made in error. These transactions will have “GOOGLE*ADMOB” as the description for the credits.
We will be processing the correct refund in early January 2014 for the correct amount owed to you. You will see a separate transaction for this refund amount on your January or February bank card statement.
We apologize for any inconvenience this may have caused you.
If you have any questions about this communication please check out our FAQ’s linked here.
""" Dear AdMob Developer,
Last week, we wrote to let you know that on December 19th 2013 we would initiate refunds to you for unused legacy AdMob advertising credits. Today we are writing to let know that between December 19th and 20th we inadvertently processed refunds for more than your unused balance. In some cases, customers will see multiple refund amounts on their bank card statement.
To correct this error, we have reversed these incorrect refunds with corresponding transactions for the same amount(s). These corrections have been processed on December 23rd and December 24th to the same bank card that the initial refund(s) was processed to. This means that you will see one negative and one positive transaction on your card statement for each refund made in error. These transactions will have “GOOGLE*ADMOB” as the description for the credits.
We will be processing the correct refund in early January 2014 for the correct amount owed to you. You will see a separate transaction for this refund amount on your January or February bank card statement.
We apologize for any inconvenience this may have caused you.
If you have any questions about this communication please check out our FAQ’s linked here.
Sincerely, The Google AdMob Team """