US Bank review: Credit card improper ageing of credits on account.

I accepted a balance transfer offer with USBank on 5/5/26. This offer became a contract to borrow money for a zero % interest until January 2027, for a 4.99% fee. I followed all of the payment terms for the balance transfer agreement.
On 7/17/26, I used the credit available on the card to pay for an emergency veterinary bill, that was reduced by issuance of a credit
to my account, after the emergency appointment. That credit was received along with the charge from the same Veterinary Hospital billing.
When US Bank received the credit, it was aged into the balance transfer, rather than the current activity. After 4 calls to customer service, and a request for a supervisor to correct this mistake, I was told this is the way they do business. This seems illegal to me, as they are reducing the total balance of the zero interest balance transfer that I already paid a % fee for, so they can charge me 28.47% on that credit of $446.99. The full amount of the Veterinary Bill was $4,000 less the credit of $446.99. This action is wrong. A class suit against this bank must be initiated immediately. Please investigate this illegal action.