How long shall I wait after the deposit with no explanation before contacting them (I assume it will by snail mail). I'm prepared to return it if they made a mistake but don't want to wait on the phone for ever.
Just wait for the letter of explanation that will come in a couple of weeks ... when you know what they changed it may all make sense.
It's a 20% hit for not following up on excessive refunds. I can spend $100 other ways.
Check over your return. Did you enter an Estimated payment or Extension payment wrong or on the wrong line? Or have a typo in withholding? Did you have a large refund? Maybe they added interest? What are you talking about a 20% hit?