I have had a multiple variation listing eg same top in 3 sizes

One of the sizes sold in October this year Size 12 

I was horrified a couple of days ago to find when the item relisted it relisted with the Size 12 still available.

A Buyer purchased it.... 

I contacted Customer Support by email advising re their error as the listing should have stated Size 12 was OUT OF STOCK obviously As I still have the details re the sale in October!!!!

Ebay reply was that is was not a technical problem on their part and I should from now on watch my stock levels when they are getting low!!!! They said when an item relists as "Good Till Cancelled " nothing will change.

BUT IT DID.... maybe I did END the item with the Free listings offer... and then of course relisted .  SHould this make a difference if the item had already sold and the listing then stated the Size 12 was not available.  Does it revert to the original listing if you END a listing instead of just letting it click over ????

Has any other seller had this same problem as EBAY has been no help at all in telling me how this happened!!!

Of course I immediately Refunded the buyer and sent her an apologetic message. BUT I will also get a defect against my account that I know is not my fault.

Do other sellers when ending listings etc check when they relist that the number sizes etc are correct?

Hope someone can enlighten me      thanks