On your iPhone, go to Settings > Messages > Send & Receive. Select your Apple ID and tap Sign Out. Then go to Settings > FaceTime, select your Apple ID and tap Sign Out.
If the phone number that you want to remove belongs to an iPhone that you can't access, change your Apple ID password. This removes all phone numbers from your iPad, iPod touch, and Mac. Calls or messages for the removed numbers won't appear on those devices anymore
Sign out of every Apple service and device that uses your Apple ID, except the one you're using to change your Apple ID.
Go to Settings > [your name] > Name, Phone Numbers, Email.
Next to Reachable At, tap Edit > Delete.
Tap Continue and follow the instructions.
After you enter the mobile phone number that you want to use as your Apple ID, a verification code is sent to you at that number. Enter the verification code from the text into the fields provided.
a) What model do you have?
b) What iOS is installed?
c) Have you tried a factory reset?
d) Except for iMessages, do calling, SMS/MMS, and data work?
Had the exact same problem. After wiping out my settings five times did nothing, I finally had to call apple support. They took my appleid and number to reset something on their side and the activation worked!
Make sue your data is is working can you use Safari and successfully go to a website?
if not try to reset network settings under General then Reset then reset network settings