Brand new iPhone 15 Pluses - and now My husband's calls to ME goes straight to voicemail AND vice versa.

I ported my husband's number from AT&T to my Verizon account. Our respective numbers are the only two on the account.

He activated a new iPhone 15 Plus and quickly noticed that calls to me go straight to voicemail - but calls to any other contact work as expected.

Two days later, I upgraded my phone to iPhone 15 Plus. Now, when I call him, my call goes straight to his voicemail. Calls to any other contact work as expected.

How do we fix?