This will probably require a face to face help with a friend.
But you can try the following:
Ensure that they have your correct phone number.
Check your messaging app to make sure that none of those contacts are blocked or marked as spam.
Go to your apps, find the Message app. Go to storage, and clear cache.
Restart your phone and see if you get any.
Only as a last resort, would I recommend a network reset, but it could help.
