How can I stop garnishment?

I've had a garnishment placed on my checks for a total of $1000. I paid the collection as soon as I found out about it. Now even though I paid it in full before the first garnishment even came out, they've still been garnishing my check and I've now overpaid by over $700. I called a few weeks ago and they said the garnishment had been stopped but I've just checked my paystub and another $200 is set to come out tomorrow which has me almost double paying the garnishment. What can I do? I really want the total of $900 back asap because this is just wrong!