We've been in Zihuatanejo for a couple of month and recently, the last week or so, RV.NET has been impossible to connect to--it times out. Try trailerlife.com then forums. Same username and password, same pages.
There is a few full timers on here from MEXICO. Check with them what to use. 'MEXICOWANDER' comes to mind...
I always turn my INTERNET OFF when I get close to the borders. If my setup starts using the MEXICO INTERNET connections I get a hugh ROAMING bill from my VERIZON Internet Provider...