JC.
Get your Bank account to 0, then close it and open an acccount somewhere else.
It sounds like someone has got hold of your details, and are charging it to your account through e-bay, or e-bay is not involved at all.
Your account details may have been picked up by a fake site, which is using your account....maybe you have clicked on a link from a fake ebay email, which has asked you to log in......
What does your account statement say on e-bay anyway?
(via My Ebay - Sellers account. it will have all chargable items)