How do I get my number to work on my new phone?

I got an iPhone 12 and after I transferred everything over to it from my 8, I made sure my number was there and texted a few people, then I erased all the data off of it. Then I realized I didn't put my sim card in for my phone service, so I put in the new sim card thinking it would help get my number to activate, but it didn't and my iPhone 12 is still hooked up to my apple iCloud account.