HELP ME PLEASE!! Phone doesnt work at all, I'm so frustrated dont know what to do =(

Hello! I'm Nicolas, from Chile. And i own a Xiaomi Mi4 Since March2015.The thing goes like this, since May the screen had a fringe/bar where the touch sensor stopped working, this was NEVER a problem, because it was an area that we never use. But 2 days ago, i pressed the power button to turn on the screen and put my password, but the screen went mad and showed just fringes with lots of colors, then it barely showed the password screen, then colors again and etc, sometimes it worked fine for like 10 seconds, and it crashed again. The phone started working awfully slow, i mean, with like 4 seconds delay for EVERYTHING, i couldnt use it!!. Sometimes it worked just fine then the screen went mad again, with fringes and dots and black or blank screens. I never did hit the phone in the process, not any kick, nothing, the screen just stopped working, all black. The next day i changed the screen (because i thought there was a problem with the screen cause it was previously with an issue, and i thought the ultra laggy system was a problem with the screen or something, that the incredible lag/delay was because the screen). And the thing is when i changed the screen, a brand new one, the exact same thing happened, nothing works, it is alive because i can screencast the phone on my laptop, but it keeps running incredibly slow, it is too slow i cant even open whatsapp without waiting 2 minutes... I cant even put my password smoothly, because it is so laggy and delayed, that if i press the number "1" it shows up on the screen like 4 seconds later... And i mean it shows up << on the laptop screen>> (not to forget the brand new screen doesnt work neither)... So it is a problem with the processor? the ram? the adreno 330? what? Please i need help, i cant afford a new phone =(.

Plus info: Everything seems to be connected alright, i did the replacement myself watching lots of videos, and everything is simple and i think well done, the phone is still alive, but controlling it by the laptop, screen doesnt work, wifi doesnt work (its like there is no adapter anymore...), 3g signal doesnt work, it does not even recognize my phone company it says no service, I controled it by the laptop and now is playing music at full volume...

I didnt know where to post this, sorry if misplaced.

HELP ME PLEASE!! I would be so thankful! =(