Most garnishments cannot take more than 50% of one's income but income is specifically defined. Assets are another story. Usually a proper order can go after assets, such as bank accounts, to the full extent of the order. Sorry.
I had a similar situation once. I went to the office of support enforcement and talked directly to a support officer. He sympathized and worked with me. Might be worth a try. Phone calls don't seem to work as well until you have a specific person to talk to, case number, phone extension.
Yes Kurt the State can do exactly what they have done. At some point in time you need to file a petition to modify the current support order due to a substantial change in circumstances per state law 750 ILCS 5/510.