mobile

hello, so it all began with the lollipop update, i wanted it on my new phone (less than a week old), so i've read everything i can about flashing the G2, and i guess i did nothing wrong (i used normal flash instead of CSE the first time), but i didn't back up my original ROM and that's the problem, so the KDZ installed normally, but when tried to configure the phone, the touchscreen went crazy , exactely like this https://www.youtube.com/watch?v=hYwumfkokOA. so i downloaded a 4.4.2 kitkat rom, but it didn't correct the problem, i used an OTG and a mouse to use the phone, and i found out that my IMEI is "null", and there is no signal at all, plus the phone heats up and the battery drains really fast, and some apps like the browser freeze when i open them, i tried at least 5 roms, and they all have the very same problems.
then i tought maybe my phone isn't a d802, so i checked my IMEI on every IMEI check website, and they all told me it's a D802, but when i removed the back cover, i found "D800 0815" written under some sticker, and i'm afraid that i'll brick my phone if i try the stock d800 firmware, and it's android 4.2 while my original firmware was 4.4.2, i even took my phone to a repair shop but no luck, i'm really confused and can't replace or buy another phone, all my savings went into this one, and this forum is the only place that can help me, so please, if anyone has a solution help me

TL;DR: my touchscreen went crazy and my IMEI says "null" after i tried a lollipop update on my LG G2 D802