Buy some Iron Out or Super Iron Out and follow the instructions on the label to redo the white clothes with some of it in the washer.
Call Art and tell him he has 10 days to come out and see what's wrong or you'll see him in small claims court where he can explain to the judge why he can't come out because you did the plumbing to install HIS softener.
FIY, if he didn't program the unit for you or tell you how to program it and what to program it with or to, it can't work right. You should mention that to the judge also.
I think the unit is too small and you probably need a backwashed turbidity filter in front of the softener to protect it from dirty/rusty water from the well. He should have known that.