Simply take your codes and convert them to physical cards at any SB store then either add them back to your account or use them as is. Old code is gone, problem solved despite the fact there never was a problem.....other than supposedly for you.
Note: This will not prevent the new physical cards from being shut down by Starbucks because they can track the codes but it will stop fraudulent use by others who may have your codes.
lol..... the person sold it to you have the code.....