Out of country, whether WIFI calling is still free?

I am visiting my mom in China now. My plan is the $30 per month - 5 GB plan. (The plan was purchased in the USA ~ 3 years ago. I keep use it for more than 3 years now.)

I try to log in my bank accounts on my laptop to pay bills. But the banks require me to input a code send by text for verifications.

I turn on the WIFI calling and I did receive the texts from my banks in the USA.

I wonder whether this is free? If not, how much it cost?

It takes more than 24 hours for my cell phone be able to receive the texts from my banks in the USA since I turn on the WIFI calling. Some banks told me: “Your Online Banking account has been locked for security reasons. To unlock your account, please call Online Customer Service at 1-800-XXX-XXXX.”

I wonder whether I can use my cell phone (a US phone number) to do the WIFI calling to my US banks from China? If yes, whether it is free?

I also have several voice message in my cell phone. I believe they were come from my banks or credit cards in the USA recently. If I listen these voice message, whether it is free? If not, how much it cost?

If someone call me from the USA to my cell phone in China and I answer it by the WIFI calling, whether it is free? If not, how much it cost?

Hope for the reply!

Many thanks!