Hello XXXXXXXXXXXX,
I cannot know exactly what has happened, but I suspect you have been the victim of an unscrupulous debt collector. You need to make sure that there was a proper judgment, signed by a judge. The papers should have been served to you prior to court. If all this is true, then you should be able to calculate the proper interest from the link I am providing. There is a legal amount for judgements and that's all they can charge.
You have paid so much---far too much, I'm afraid. You need to make sure all the above is correct. If not go to the court where the judgment was ordered, or where it should have been ordered, and take all your paperwork showing what is happening. You should be able to file something with the court asking to stop the garnishment. It may be beneficial to get an attorney to take care of this for you. If you gather all the info, it would not be expensive, I don't believe.
I am so sorry this has happened, and I certainly hope you can get this stopped. I would even suggest you consider looking into filing a suit against them for violating the Fair Debt Collections act if it is found that they violated the law.
Good luck.
Lawyer (JD)
Juris Doctorate Degree