Country code missing from International Calls

I have a user with an iPhone 6S on AT&T, he has the latest update installed and he is physically located in the US. I don't know if it's effecting international calls across the board but I assume yes (he only deals with Mexico.

Anyway when they get calls from Mexico the country code is getting off. Based on the area code Mexico the number should start +52 868. Instead the number is coming up formatted as (868) 111-2222 which shows on caller ID as Trinidad and Tobago. Which apparently is correct the 868 area code can be dialed from the US as a normal call to get Trinidad.

So the real question is "Why is the country code +52 getting cut off?"

This is happening to calls from landlines and cell phones.

Any help is appreciated.

Thanks,

Kenny