iMessage combining two phone #s for the same Contact

I have my partner’s personal and work mobile saved in their Contact Card. Anytime I go to iMessage them, I have to select their personal number before sending each individual text or else it defaults to their work phone.

I have tried starring their personal mobile number and pinned the iMessage thread with their personal number. I have also tried separating their work and personal mobile numbers into two differently named Contact Cards, but iMessage still combines them. I’ve tried deleting both iMessage threads with both numbers from my iPhone.

Now, when I go to text their personal message the blue iMessage shows as sending forever / never fully go through. My sent iMessage will then appear in an iMessage with my partner’s work mobile number instead in a separate thread. Has anyone encountered this issue after the most recent iOS update? Any tips for troubleshooting? Thanks in advance!