Hey LydiaStevens,
We'd be happy to help out with the iMessage activation issues you're facing. If you can't activate iMessage for use with your phone number and Apple ID, check to make sure you can still send and receive SMS without issue.
If not, this indicates an issue on the carrier side of things causing this to occur, as the ability to send and receive SMS is required for successful iMessage activation. Without this, it could fail. You should contact your carrier if SMS isn't working.
If it is, the following steps are best equipped to assist with resolving activation issues with iMessage:
Check your device settings
1. Make sure that you’re connected to a cellular data or Wi-Fi network.
2. If you're using an iPhone, you need SMS messaging to activate your phone number with iMessage and FaceTime. Depending on your carrier, you might be charged for this SMS.
3. Go to Settings > General > Date & Time and make sure that your time zone is set correctly.
Turn off and restart iMessage and FaceTime
1. Go to Settings > Messages and turn off iMessage.
2. Go to Settings > FaceTime and turn off FaceTime.
3. Restart your device:
* iPhone
* iPad
* iPod touch
4. Turn iMessage and FaceTime back on.
This is outlined further here: If you can’t turn on or sign in to iMessage or FaceTime - Apple Support
We hope this helps out.
Take care!