In relation to your mobile billing question (and please forgive me if you've already tried all this)
Go to Google Play Store
Click on your image top right (in my case it is the first letter of my name)
Payment Method and Subscriptions
Payment Methods
In my case, half way down the screen there is an option for Vodafone Billing
I am not employed by Samsung nor do I receive any remuneration as a Samsung Members Star.
My device is an S25 Ultra.