Hi
In order to solve this error, please complete the following steps:
- Note down the number/s you’re having this issue with
- Completely remove any contacts containing those numbers
- Delete all text message threads and call logs involving those numbers
- Power the device off, and back on. (If an iPhone, head to Settings>General>Reset>Reset Network Settings)
- Try sending a text directly to one of the numbers, before saving it as a contact
If this helps, please mark this answer as an accepted solution!
Thanks,
Charise