EBay double charge for missing posted item

[since108]

Hello,

I sent a parcel via eBay Royal Mail labels. The parcel went missing. I have refunded the buyer. I have since received an email from eBay saying that my account is overdue with the exact amount that I have already refunded the buyer through eBay. 

all transactions have been done through email, postage order cancellation & refund. 

Im now being charged twice, please help 

[john1297576]

I thought that this was what buyers paid for, and if something went missing then ebay refunded.

If this is not the case what are buyers being overcharged for?