If I were you brother I would write a short letter saying that you would not like for this person to be your caregiver any longer (no reason is needed). I then would mail this letter via certified mail with a signature required. Then just keep a copy of the letter and the receipt for the certified mail. This will be enough to show anyone if any questions were ever to come up.

Editing post to add something....
1. Just because you got a discount doesn't mean that you have to stay with this caregiver if you don't feel that they are providing adequate "care".

Feijao