You'd do better by finding out more information about your Mexico ISP and what are their requirements than asking here. Find out if you're required to use their gateway, how that gateway is connected, and whether or not the gateway can be put into "Bridge Mode" or "Passthrough Mode" to support your own router.
Most likely your Cisco is all you need if the gateway can be put into Bridge Mode, OR you have fiber service with an ONT and no requirements to use their gateway (just return it to them). But checking with the ISP is easier than us guessing what is needed from them.