My old iPhone 5c isent working?

I got an iPhone 5c in green. I dident pay my bill so they turned it off. I haven't charged it in like 8 months almost 9, because I just found it. But I charged it all day and it still won't turn on. Did att make it so it won't even turn on? If not how can I make it work again?

They did make it so that it doesn't turn on.