I checked your transaction history, and the only refund I see is the refund you processed for another client last 20-October, in the amount of $25. I also checked your account and do not see any chargebacks. Could you please share the Contract ID you are referring to so that I can look into this for you?
I would like to confirm that the payment for the first and second milestone are intact, and is showing on your transaction history. You can go to your Transaction History to check the payments that were made on this contract. If you are referring to the third milestone, it looks like the milestone was created, but never funded. If you were meant to be paid for this milestone, you can contact your client directly to discuss a bonus payment.