"800 numbers" (and "877-", "866-", etc) only work if the call is made from "Country Code '1' " (US, Canada, and a few odds and ends). Antigua lies in Country Code "268".
You'll need the non-800 equivalent phone number to get through 😞 (and pay international rates).
Alternatively if you have a US or Canadian cellphone provider and set your cellphone to "WiFi Calling" via the ship's WiFi, that should make your call be coming from "Country Code '1' " 😉