Creditor Refused Payment

I live in Illinois, but my creditor is in Iowa. I owed $115 to my doctor's office. I mailed them a check for the full amount, but they refused to accept it because it was not made out to the collection agency to which they have referred my account. Can they refuse the payment because the check is made out to the doctor's office instead of the collection agency? Am I in any way obligated to the collection agency?

[VeronicaGia]

If this has already been sent to a collection agency, you have to make the check out and send it to the collection agency. The doctor cannot take your check.

Make a new check out to the collection agency and send it to them. Tear up or void the old check.