Dear random user,
In my experience, this is the kind of problem that comes up when someone decides to use magic to hurt someone, but has no family history or training, and takes a kind of "random" approach to it, as your screen name perhaps indicates.
I often hear from folks who just kinda-sorta-maybe do it, then kinda-sorta-maybe dispose of it, then realize, often rather rapidly, that magic is more than a child's game of make-believe and that their kinda-sorta work had real consequences.
So you threw the doll in the river, which is indeed a traditional way to get someone out of your life. And it worked. The person is now out of your life.
If the person is miserable, due to your curse, and you "just want their misery to stop," you will either have to fish the doll out of the water and dispose of it another way, such as in fire, while releasing or breaking the spiritual link, or go back to the river and release the spirit from the doll some other way, such as through prayer. I would consider then a Hyssop tea and bath for yourself and a recital of Psalms 51.