Grist?

[NewHope]

What does "grist' mean here?

Is " fees no one tells you about to work left undone " a thing? From the thing to harassing phone calls...?
If the writer said " fees no one tells you about work left undone ", I'd got well. But what "to" meant here?

Context:
The survey of state and local consumer protection agencies was conducted by the National Association of Consumer Agency Administrators (NACAA) and the Consumer Federation of America (CFA).


It found that the grist for grousing ranged from fees no one tells you about to work left undone to harassing phone calls, deceptive advertising and defective goods.

[Francois]

grist for grousing = reasons to complain
I think there are 3 parts actually:
from fees no one tells you about to work left undone to harassing phone calls, deceptive advertising and defective goods.

FRC

[NewHope]

Thanks Francois.

What does " fees no one tells you about " mean?

[Francois]

Hidden costs or charge eg. when you withdraw cash at an ATM, most bank charge you an extra fee of about $1 if your account is not in that bank.

FRC