iPhone 8 Plus will not turn on after charging?

My iPhone 8 Plus was at 70% when I woke up a few days ago and I went to charge it before I left the house, 30 minutes went by and I decided to go get my phone. When I picked it up it would not turn on. I tried all the various force restart methods and nothing worked. I tried plugging it into iTunes and it wouldn’t pick up my device. I took it to apple and they said that the battery wasn’t the problem and they tried to charge me 400$ for a refurbished replacement, but that’s what I’m trying to avoid because I know there is something else that can work. Any thoughts or suggestions?