Switched from Android to iPhone, iMessage not working

I recently switched from an Android phone to an iPhone 14 Pro. I was a previous Apple user with a Mac and an Apple ID linked to my gmail address. I switched partly because my father has an iPhone and he regularly goes to a cabin where there is wifi but no cellular service. I was unable to contact him with my Android phone via cellular/SMS. He would text me from his iPhone or iPad to my Mac using iMessage. After I switched to iPhone, my texts to other iPhones show up as blue/iMessage. But my texts from my iPhone to my father's iPhone are still green/SMS and are not received when he has no cellular service. I think it's an issue with how our Apple accounts and iMessage are configured on our various Apple devices. When I send a text to his icloud email address from my iPhone, it sends as blue/iMessage and he receives it on his iPhone and iPad. When I text to his phone number, it sends as green/SMS (and he does not receive it if no cellular service). I deleted him as a contact on my phone, deleted our text conversation history and signed out of iMessage on the Mac, but am still having the same issue. Any advice?