Shift Key and Mouse problem after Apple Support

Hi guys!

I'm kinda angry rn, so I'll explain my situation.

I sent in my Macbookpro (mid 2014) A1502 in for repairs due to the screen delamination problem I had. The service was speedy and the screen ended up being fixed to perfection.

However....... the person who fixed my Macbookpro changed my password, set the hint to "Rick Roll Nig**", and somehow set the shift key to be continuously on. This led me having to put in a usb keyboard and change my password. But the shift key problem is still there, so i wiped and reinstalled OsX Yosemite 10.10, sadly the problem persisted.

So now..... although my screen is fixed, i have to press Option button to prevent my mac from going into safe mode every time i turn on my computer, and for some reason, the shift key is affecting the rest of my keyboard by freezing it up sometimes and also making my mouse always right click.

I installed Karabiner and figured out that it is a problem of the LShift key (right shift is fine). The key feels fine and there is nothing beneath it that would make it continuously on...

So....

Q1: is there any fix to this (excluding the use of Karabiner and disabling the LShift key). I would like a solution that fixes my keyboard, not using a third party to block or bypass the problem since i would still have to exit safe boot every time i start the computer.

Q2: i got my mbp fixed a few days before my limited warranty expired, and by the time i got it back my warranty is now over. However i looked on the apple repair sheet saying if my product requires further repairs within 90 days of this repair due to issues caused during the service AppleCare service will repair them free of charge, i assume this would fall under the category and if worst comes to worst i can send it back in?

Thanks!