The older RW phones worked only on the Sprint network. Your newer phones (assuming you bought them from RW) are on the T-Mobile network. Sprint uses CDMA cellular technology, and T-Mobile uses GSM. But, they are two entirely separate cellular networks. So, you may have coverage in some place with the new phones that you didn’t with the old phones, and visa versa.
If you didn’t pay attention to any of this when you bought your new phones, don’t blame Republic. Republic is not the network. Take some responsibility.
Also, this is not Republic’s customer service forum. This is the user to user discussion community. To deal with tech support/customer service, you need to open a support ticket.