Why wont my note 4 edge get reception

I have a galaxy note 4 edge on android 6.0.1 that I bought off of eBay for $50 and it the reason it was that cheap was because it cant get reception for networks. I got it to the point where the reception comes for abut 5 seconds then goes away. I wanted to know if there's anything I can do software wise to resolve the issue. Before you ask it came factory data reset and I cleared the cache partition and I also added a mobile network name ( If you know what I mean by that). Anything would help thanks.