Is This allowed???

I had a small bill (100) due to the SurgiCenter here...It's next to the hospital and where they do outpatient surgery. I should have paid it, but for various reasons, I didn't. They sent it to a collection agency about 4-5 months ago. Last month, I had 2 surgeries for cataracts. They contacted me beforehand and said that my co-pay was $100 for each operation and that I would have to make the $100 payment on or before the day of the operation.
After I had the operations, I receive bills from them for $150 for each operation. It seems that our co-pay has increased. Okay, that's understandable.
However, they took the first $100 that I paid and applied it against my past due balance from before. I did not think that they were allowed to do that since they had already "sold" the account to a collection agency. Both the original SurgiCenter bill and the CA are listed in my BK, however, operations were in September and BK was not filed until Oct.
Is what they did legal? If so, can I correct my credit report to show it as paid, and if so, wht do I say to the CRA's re: the collection agency.
It seems to me like the SurgiCenter got paid twice...once a portion of the bill when it was sold to a collection agency and second when they took my check for this recent operation and applied it to the past due bill.
Anyone ever experience something similar? Any advice. TIA, Art

Since they did this before you filed bankruptcy, it is legal. They had a bill due to them, and when they rec'd funds they applied it to the oldest bill first.

I could be wrong, but since this was before you filed, i would say that it's perfectly legal

They may not have sold the account originally, may have just outsourced it.

Beyond that, since the surgeries (and most recent balances) happened before filing, you should be ok. Just make sure that the facility is listed as a creditor. If they are already, you probably won't even need to update anything.