Busynana,
1) Revisions to your active listings should be done directly through eBay. When you click the "Revise Item" link on the active listings page, it simply directs you to the eBay "Revise Item" page, so I'm unsure how you ended up with multiple listings.
For future reference, to revise your listings, just check the box next to the listing on the active listings page and click "Revise Item".
2) The duplicate listings should be cancelled through eBay and eBay can be contacted about a refund. They're generally pretty good about giving refunds if you explain that you accidentally double posted some items. It is best not to say that you use a 3rd party listing service when contacting eBay for a refund.
Once you've cancelled the duplicates on eBay, you can make them hidden in your Auctiva store by going to Auctiva -> Store(tab) -> Edit Items . On this page you have the option to make listings hidden. Listings that are hidden will not be displayed in your Auctiva store nor will they be displayed in your Auctiva store window the next time it refreshes...it does so about every 2 hours.
I hope this helps=)
-Mike