<prompt> Human: Had an invoice arrive in the mail for 134.23usd for my sons surgery. Paid the bill promptly with my hsa for the exact amount of 134.23. Today, six weeks after the payment. I received a collections letter stating that I owe 134.23. Called the hospital and they acknowledged receiving the payment. However, they paid a different invoice of their choosing. This doesnt make sense to me for a few reasons:1. They require an invoice number to process the payment. 2. I have not received any further invoices from the hospital or my insurer. I disputed this with the creditor, but Im afraid that they will find that it is a valid debt. This is going to comedown to the hospital and while I have records showing the payments Im not sure if moving the payments to a different invoice is legal. What are my next steps? I can easily pay the 134.23, but its the principal that bugs me.  <response>: You need to work with the hospital to get the payment properly credited and the collections agency notified of this. 