Got a call for a 10k grant, scam?

So i got a call from 202-470-4580 claiming to be from the US Government Grants Department, saying that I had been randomly chosen to receive a 10k grant. Im supposed to make a $99 donation to the American Indian Charity Foundation via western union to receive the grant. I decided to hear what the guy had to say, but I ended up giving away my bank account number and routing number. I know that was stupid. I havent sent the $99 dollars yet and probably wont. Has this happened to anyone else? What should i do know that I have given away my bank account and routing numbers? I dont want to get scammed :(