The mail system in Buenos Aires is HORRIBLE. Half the time I never got things sent to me via regular mail. The only way was if they sent it via a trackable source like Fed Ex, UPS or Priority mail with delivery confirmation from the USA was pretty good.
But several times when I had things mailed regular mail it took months in some cases to get.
The best thing I found was using something like
www.virtualpostmail.com and even having things sent to the USA, they would scan and email me all my mail and then anything important I'd have them send me either via Fed Ex or USPS Priority Mail with delivery confirmation and I'd always have it within 7 to 10 days.