First things first, have you been able to connect the base unit directly to your home router via the RJ45 LAN connection?
By default MOST ISP router run an internal LAN (Local Area Network) with a 192.168.1.XXX sub-net, if this is a used unit you need to confirm that it's using the same (flat) network as you have internally and that it hasn't been setup for a 10.x.x.x address space. You also need to confirm the unit is set for DHCP (see definition below) and not a static as that will also cause issue with a used apex (the default is DHCP and not static).
DHCP stands for Dynamic Host Configuration Protocol. This is a method for automatically configuring TCP/IP network settings on computers, printers, and other network devices. Using DHCP, the computer user never has to make any TCP/IP settings.