When I had irrops in Funchal in January I was texted a link to use their own Web chat (because I refuse WhatsApp). It was very successful and would work over hotel and airport WiFi. And is capable of holding when moving across networks. They really should consider that.

As a point of reference I had a last minute booking (booked Thursday for Sunday) with KLM where the ticket was not issued, both the app and email booking confirmation bleated to get in touch about ticketing. Took a few phone calls but it all worked in the end.