Hi nell198,
Try going to Settings > Messages.
Turn on iMessage.
Can you send and receive texts now ?
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If you still need help:
Apple Support have an article online that may help:
If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support
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If nothing so far has helped:
:
Try reaching out to Apple Messages Support ...
Scroll to the "Get Support" link at bottom right on the webpage that opens from the link below.
Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support
Or
Apple phone numbers around the world
Contact Apple for support and service - Apple Support
All the best :-)