I filed my taxes on the first week of March and got the notice last week. I couldn't get them on the phone. So after freaking out a bit, I realized my mistake and realized why the number on the notice didn't make sense to me at first. Basically I paid my taxes (the number I got when filing) but the notice I got was sent before that payment was processed. Anyway, once I figured out all I owe was the $1400, I went into my account and paid it.
