There are exceptions to every generalization, so I’ll just say that I remember when @jpflavin1was on the Camino de Madrid. He had emailed and called Ray and Rosa a number of times to see about staying in their place outside Manzanares, no luck. He WhatsApped me in the US to ask if I had any ideas. I told him to send a WhatsApp, and he had a response in minutes.
I believe that Susana of Torre Vilariño on the Invierno also has the policy of not responding to calls, but will respond to whatsapp messages.
Not to say that calling is a bad idea, and it’s what you will have to do if the accommodation has a land line, but the other advantage of using WhatsApp is that you have an actual record of your communication in case there’s a mix-up.
I always add as many contacts as I can before I go, so when I’m actually there, I can just pull up the contact (I always include location in their name, so I can pull up all of the places in Quiroga, for example) and send a message. Adding them to your contacts is a bit of a pain, but I find it much easier to arrive in Spain with the numbers all there and ready for me to use.