iphone wi-fi trouble

I lost at 5s due to water damage and recently purchased a used 4s. It connected fine and worked great, until I went and had it activated. I brought it home and it refuses to connect to my home wi-fi. It worked before, but now I just get a incorrect password error. It connects to other networks, but not the one that matters the most. I'm running iOS 8.4.1. I've tried everything, reset my network settings, reset my modem/router, and even did a full factory restore we nothing working. Anyone have any clue how to fix this? Can't afford to run on data constantly! Thanks!