Do banks protect you against fraudulent money orders?

Ok, so 4 years ago, when the Nigerian scams were on the rise, I put up a Craigslist ad to sell an entire collection of rare action figures... I got a response from a buyer outside of the US who had arrangements with their own "private shipper", and they would mail me money orders from their US address, you know the typical scammer protocol. Long story short, the guy sends me four 500 dollar money orders, which for my figures actually seemed like an accurate price. I deposited them into my Bank of America checking account, and they held the funds for at least a week and a half to 2 weeks. Finally, the money orders cleared, and I had access to all of the funds. I needed the money badly, so I spent most/all of it the same week the funds cleared on bills and various debts. Low and behold, BOA sent back the money orders with a huge red stamp on them that says "COUNTERFEIT", and I checked my account only to find out I was -1,200 dollars. BOA kept saying I owed them that money, and that it was my fault. I don't understand how this was my fault in any shape or form. The bank held the funds for an extremely long period of time, isn't it THEIR job to decipher fraudulent currency as opposed to non-fraudulent? I immediately stopped banking with BOA and blew them off, because I felt as though I was not responsible for their lack of attention to detail. Just recently, they sent this off to a collection agency, and now they are haring me to pay this money, AND it's negatively impacting my credit report big time! Do I have any rights or options to resolve this? Or do I just pay them the money? Someone please help with advice!