Can Superior Asset Management sue me?

I have been getting calls from Superior Asset Management for several months and my first payment attempt to them was returned for NSF. Last month, I was able to workout a one time payment that would close the account. The payment was taken out of my bank account and then returned to my bank account. The funds were there and I am not sure why that would happen, but the supervisor from Superior was very harsh with me telling me that it was returned for NSF again and they would not deal with me anymore and would contact a lawyer in m area to collect the money and it would cost me a lot of extra money. The debt was owed to Bank of America. Can they sue me for the money and how much extra would it cost? And do I have a valid argument that the funds were available in my account and they were taken out and returned for an unknown reason?