The bank teller "says" she gave me too much money

I went to cash my payroll check where my employer banks. I do not have an account with this bank. I told the teller that I did not want any $100 bills. As she worked on getting my money together I noticed her in and out of the drawer a few times, taking money out and putting money back in. As she counted out my check to me (I watched her, but did not count along with her) she stopped, referenced back to my check and finished counting. I took my money and left. Now, mistake on my part is I don't usually recount the money, I did not on this occassion. I went on with my weekend, grocery shopping and buying household items, and things for my daughter. On MONDAY I get a call from my co-worker saying that the lady from the bank needs me to call her. I call and she says that she gave me $100 too much. She originally stated the gave me 3 $100 bills and $400 in $20's. No she didn't. Then she said she meant to say she gave me $300 in $100's and $400 in ones. No she didn't. The biggest bill I had was a $50. My question is - I don't know for a fact if she did or didn't give me more money since I didn't count it. And by this point, even if she did - the money has been spent. Who is at fault here and what do I do?

 

Thanks for the replys. This lady has called me at work twice now about this. I guess I worded what I meant wrong when I asked who was at fault. I basically meant, am I responsible leagally to repay money that I don't even know if I was given? I don't want to keep money that doesn't belong to me, but I also don't want to come up with a hundred bucks for someone elses mistake. I feel like I'm the last person she remembers and thinks I'm the one she gave it too.