Multiple payments for tablet

Hi. When I powered up our tablet today it signaled me that our subscription had expired. My wife reminded me (after I paid the ~16 dollars....) that she had done the same thing back in November. I verified the Google play store receipts and she was correct. The 16 bucks is for a years subscription. How do I get my money refunded and how do I prevent this from happening again. We don't use the tablet very often so it seems if it is off for a while when powered up it defaults to an expired state.......