How do I stop message sharing?

I have a new PERSONAL iphone (16 plus) and an old WORK phone (SE) that I have somehow screwed up when I activated the new PERSONAL phone. Now, text messages are being sent from the 16Plus but showing up on my contacts phone as from the work SE. So for the last few days, I keep getting "who is this" from my friends that were not contacts on my SE but that's the number it's being sent from. Help. It's so obnoxious.