Welcome to the Community!
I’m a customer (like you), so I don’t know why you would be told the new phone would not work in your area especially since:
The Moto G7 Power is capable of working on either of Republics networks.
Please use the link below to check and see what SIM type you are currently using (GSM or CDMA)
If your Moto E4 is GSM you should have no trouble moving it over to the G7 Power.
If It’s CDMA, let us know and we’ll point you to how to get that SIM.
Added: As far as being able to buy the G7 Power, unless others here on the board have more advice (or know why you would be told you can’t purchase it), I would open a ticket and explain you’re a current customer and want to buy the Republic phone but are having an issue with the purchase.
Hope this helps.