Someone filed taxes on my name last year and I can't file this year how do I fix that?

i went to hr block to do my taxes because i was going to get a big return, usually i dont get a return, well, usually is like $50 dollars, but this year since i got a kid i will get $1500 which i am very happy about. so i go do my taxes and the tax lady tells me i can't file my taxes this year because someone already filed my taxes last year with my name.

i am not sure what to do, the lady at the tax agency told me to call the irs and talk to them about it maybe they can do an investigation on the problem.

i was hoping you guys can help me. how can i fix this. please help