Lies on tax return

Hi,
I only reason, I filed my tax with H&R block as they confirmed me with 4400$ return and for that they charged me $400.
The amount I received back is $580 less then they confirmed. When I asked them about it, there answer was pathetic. They said it is what it is we can't do anything.
When I asked what is wrong in calculations they said, they might have different formulas than us. They didn't even entertained me properly.

This is so pathetic.