Just to rule out something went wrong with restoring the contacts (number format or else) … Did you try to enter a phone number manually and send a text to it?
Edit since you factory-resetted anyway and are able to restore 
: Googling the error suggests you could try dialing *#*#4636#*#* … Test menu appears (nice, didn’t know that) … first item (sorry, german phone here, something like “phone information” I guess) … scroll down to “SMSC:” … refresh that.