Oukitel C5 keeps restarting

[AC Question]

Hello everyone,so i got this phone from a friend of mine called OUKITEL it has android on it marshmallow i think and it has a problem.At first when i got it it said unfornately settings has stoped.I have been fimiliar with same errors in the past because i have worked in a phone service.So when i saw that error the first thing that came in my mind was performing a hard reset since i couldnt do a soft one because i couldnt acces the settings.So after i did that everything seemed good the errors was fixed i could open the settings just fine but after a while,after getting my gmail on it and went to open play store it said unfornately play store has stoped.I was kinda confused cause most of the time a hard reset would fix this kind of errors but anyways.I did the hard reset 2 more times and again the same thing.I also tried a soft reset.After that i was like idc ima just use aptoide,so i disabled play store downloaded aptoide downloaded instagram and facebook and than the phone froze and than it restarted over and over and over and it even got really hot.I didnt belived there was a hardware problem so i flashed it with sp flash tool and its official ROM.And guess what...nothing happens.Now can anyone please tell me how can i fix it without getting my hands into its hardware cause ive never opened this kind of phone before and it will be really hard to find replacment parts for it as it wont be even wothed.Please comment me your ideas.Thank you.

P.S
I am like an average english speaker so sorry for all the grammer mistakes.