Hi and welcome to the forum.
First: I agree I would not recommend this phone, but then I never recommend anything 
A new bottom module may help, but ensure you clean all the contacts when you dismantle as they can easily tarnish.
See cleaning ideas for the ‘solder’ contacts in the following post . . .
The blue ones in that image
Once you have a new bottom module, and if that resolves the issue, you can try a more intensive clean of it and maybe get it to function as designed.