After you file

I received a letter stating I owe $850.23, I only received 2 stimulus checks and I have never had to pay the IRS. I was actually going to receive around $600 back from my tax return. In total I believe I owe $1268 but my income tax was $420 which was subtracted from the $1268 and it ends up being $850.23. I’m sure it’s a mistake but I’m not sure how to fix it.