Jenna,
Perhaps your mother signed for a voluntary wage assignment. You can verify it from the papers provided by your creditor. You can cancel this by sending them a revocation letter.
You have not mentioned in your post whether your mother is capable of paying her bills or she is dependent on you. Anyway, you have few options in your hand-
Contact the collection agency and ask them to stop taking money from your paycheck. Ask them to validate the debt and then make suitable payment arrangements.
Or, you can contact with your creditor directly and inquire if they can accept the payments. Don't forget to make written agreement before paying to your creditor or collector.
If you feel the whole process very complicated and troublesome, consolidate it. credit card debt consolidation is a good option and brings lost of benefits in your way.
http://www.debtconsolidationcare.com/benefits.html