Hi there Seca1172,
We understand you're receiving unknown texts on your iPhone 7, and we'd like to see if we can assist.
If these are coming as SMS messages, they'll only be sent to and received by the phone number associated with the device.
Alternatively, if they're iMessages, check in Settings > Messages > Send & Receive to see if both phone numbers are listed under the "You can receive iMessages to and reply from" section. You can then de-select the phone number for your other device to isolate which number the messages are being sent to.
Additionally, check out the information here: Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch
Specifically, the "Filter messages from unknown senders" section may help.
Cheers!