Google are changing the Google Wallet app, and are discontinuing the Google Prepaid Card soon due to the fact it now accepts any debit or credit card.
If you currently have a balance on your Prepaid card, you have until October 17th this year to spend it.
There are lots of terms and conditions, as is usually the case with these financial type things.
All the details are in the link below for your perusal and delectation..
Google Wallet Prepaid Card Program Termination