Express Scripts Payments applied to wrong billing account ID and overcharges Saint Louis Missouri

Since May, the payments that I have been making to my partner's account statement have been incorrectly applied to my account. The first time that it happened, I thought that I just forgot to pay and paid the bill again.  With the next billing statement, I paid the total amount, not noticing that I was billed again for the same original invoice. 

The next bill received showed both invoices unpaid plus a new one added.  I collected copies of the cancelled checks and emailed them on October 3rd.  Instead of correcting the accounts and applying the payments correctly to my partner's billing ID, they charged her bills to mine.

Shortly thereafter, I received a notice that I can no longer use them for prescriptions since I have an outstanding bill that is more than 60 days old.  I contacted them again to have the invoices corrected, and am told that there is no such thing as separate billing account numbers even though an earlier rep confirmed this fact and the fact I am looking at them right in front of me. 

I went even further to communicate with them, providing a breakdown of the charges payments and account numbers, and to gather this information I looked up the prescription prices as listed on their website only to discover that I have been overcharged. 

This company is impossible to deal with and all for a few dollars.  I am not denying that I owe them money, but not on the accounts that the statements are reflecting, and not for the amount stated.  All I want is corrected billing, and for the payments to be applied to the correct accounts when I send them.  I am amazed that after 14 reps, including a supervisor on the phone, no one can figure this out.  Shutting off the ability to order medication is life threatening and overcharging is criminal.  If I had a choice for prescription coverage, I certainly would not use Express Scripts.