PayPal didn’t refund the payment fees when canceling an eBay transaction and refunding the buyer

Description

Buyer A purchased an item on eBay on July 12 and asked me to cancel the transaction the same day. I tried to cancel the transaction on eBay but was notified the refund can’t be completed. After checking my PayPal, I found that I couldn’t refund Buyer A because I had not enough funds in my PayPal account to cover the refund (I only got the amount of the payment I received from Buyer A in my account and I was required to add funds which equals to the payment fee of this transaction to complete the refund). This is quite weird because I just refunded Buyer B on July 10 without paying any payment fee (I had no extra funds in my PayPal except for the amount I received from Buyer B). On July 15, I received a payment from Buyer C and I issued the refund to Buyer A using part of the payment from Buyer C to cover the payment fee. Now the transaction status on eBay is still cancelation pending but eBay and PayPal both confirmed the refund has been issued successfully. EBay customer service rep promised me that the cancelation status will be changed in 48 to 72 hours. My question is: 1) why the refund process of Buyer A and Buyer B are different? 2) Why I had to pay the payment fee? 3) How can I get back the payment fee?