How to turn off incoming phone calls for a specific SIM card / phone number?

I moved countries and I'm keeping my old phone number just to accept texts from old contacts. This is on a secondary SIM card. However, I have very high roaming fees and occasionally I'll answer a phone call and miss the little icon that signals what number they're calling and it'll cost me $$. Also when driving, Bluetooth doesn't signal which phone number they're calling from. I'd like to just disable incoming calls all together to that phone number. It's mainly only spam phone calls anyways. Any idea how to block incoming calls iPhone 13?