Hi CoMx269,
Thanks for contacting Apple Support Communities!
We understand that you have two message threads from the same phone number.
Are they both coming through as text messages or iMessages? With iMessages, messages can be sent to you using your phone number and your Apple ID email address. This resource will show you the difference between iMessage and text messages: What is the difference between iMessage and SMS/MMS? - Apple Support
"iMessages are texts, photos, or videos that you send to another iPhone, iPad, iPod touch, or Mac over Wi-Fi or cellular-data networks. These messages are always encrypted and appear in blue text bubbles. To turn iMessage on or off, go to Settings > Messages.
SMS/MMS
If you aren’t using iMessage, you can use SMS/MMS. These messages are texts and photos that you send to other cell phones or another iPhone, iPad, or iPod touch. SMS/MMS messages aren't encrypted and appear in green text bubbles on your device.
To use SMS/MMS on an iPhone, you need a text-messaging plan. Contact your wireless carrier for more information. You can also set up your other Apple devices to send and receive messages from any Apple device."
Do you know if the person you're receiving messages from is sending the messages to your email address or phone number?
If it's coming through as a text message, the text messages are provisioned by your carrier. You may need to contact your carrier to review your account provisioning.
Cheers!