Sale gone through at wrong price which is reduced

I had an item listed for buy now $28 there was no make an offer on my listing but some how this is now in my unpaid orders and it has gone through for sale price of $20. How has the buyer got this sale to go through and what can i do about it. This is not the first time this has happened. How can I stop it.

This one? If so, it's showing as sold for $28

 

Multi-Strand Lime Green Speckled Glass Necklace | eBay

*casey*
Community Member

And just to confirm you have "Automatic Offers" enabled, I put two of your items on my watch list yesterday

 

(although offers are also sent to buyers who just look) and I've received  offers from you for both of them.