Ok so i rooted my GT-i9300T and installed a jellybean rom had that for a few days then i wanted to go back stock, i followed instructions with triangle and unrooting but i messed up and installed a international version rom so now instead of the model being GT-i9300T it reads GT-I9300 and it wont let me register my device for software upgrades and messaging wont work. it says "Unfortunately messaging has stopped". i found the right rom i need to install but now when i try to connect it to my Mac via AFT it wont recognize it no matter what i do. I've messed up and don't know where to turn??? someone please help me i'm sorta worried i've effed my brand new phone
Did you make a nandroid backup before you flashed. If so you can always restore that. If not, then shame on you.
Kidding ... but seriously, ALWAYS make a backup.
Can you connect to the play store and download apps? If so, I'd recommend installing an app called WiFi File Explorer PRO (not sure if you need the pro version or not, but that's what I have). This app allows you to transfer files to and from your phone over wifi. So you could put the correct ROM on your phone and flash it. I don't have a Mac, but all this app does is assign an IP address to your phone that you go to in the web browser on your PC, so I would assume it works with Macs. You might want to Google it first to be sure.
I hope this helps. And seriously, next time, make a nandroid.