Hi Alex,
The only thing I can think of that would cause the same item to be posted 10 times would be if you clicked "Post" and wasn't sure of the result, and then clicked "Post" or the back button again and again because each of those would be interpreted as a post command. Anyway, if you'd like us to look into this further, you can file a support case using the appropriate link on our help page.
I suggest you request a refund from eBay for the money you lost on listings that you had to cancel. They're generally pretty good about refunding money in the event of a mistake. It is best not to mention you use a 3rd party listing service when requesting a refund.
-Mike