I was a part resident in one state, worked and paid state taxes, then moved to a different state with a different job. Why do I owe excessive taxes in my old state?

I was a resident in state A for 6 months. I moved to another state and got a different job. I owe an exorbitant amount of state taxes in my old state even though I technically overpaid in state taxes according to the old state brackets. Not sure where I went wrong. Have never filed part resident before so this is all new to me.