I assume you mean that the switch plugged into a cable or DSL modem. Your service provider only issues you one IP address. The tech support answer was correct. Your internet service provider's modem is intended to be plugged into a router, which will provide you with local IP addresses for the devices on your network, such as computers, IP phones, TVs, or whatever else you're using. The router will typically have 4 or 5 Ethernet LAN ports on it. Plug the OBi into one of those ports. If you needed more than that many ports, then you can daisy chain an Ethernet switch onto one of the LAN ports on your router. Think of the switch as a dumb AC power strip, with multiple outlets. It doesn't have the ability to issue IP addresses.
Note to the troll: I am not providing a full treatise on the operation or routers and switches; just enough noob info to make things work.