Hi Shelly,
Maybe you entered too few question marks above, but you should have +54 9 2966 followed by 6 more digits. 2966 is the area code of Rio Gallegos. In Argentina area code plus local number always total 10 digits.
Now, supposing you do have a correct cell number (especially that you said you have been able to call it), there could be two reasons why your texts don’t go though:
1. While for voice calls one must use 9 before the area code (+54 9 2966), this digit must generally be left out when texting to an Argentina cell. In your case: +54 2966.
2. For texting to work between countries, international operators must have some agreements, and it seems that Argentinian wireless providers do not have agreements with most international wireless companies.
I suspect and hope your text will go through using the first solution I gave you. Let me know please.