You have quite a high feedback score but I think it is all for buying, not for selling.
I had a quick glance at feedback and it seems you have occasionally run into problems, but I am not sure if you knew or know how to solve them.
It probably pays to have a look through the help pages if you do run into a problem.
The first thing that is occurring to me is that the seller 'agreed to cancel'. I presume that was in a message?
Saying and doing are 2 entirely different things. I don't think ebay would refuse a cancellation.
A buyer cannot cancel, only a seller. I think the seller was lying to you if he said ebay refused to allow him to cancel.
I think ebay messages are, for the most part, automated. So if you kept getting emails asking you to finalise payment, then the sale was definitely not cancelled, in my opinion.
I am unsure what you mean by accidently agreed to buy 2 flashdrives. Did you buy one and then bought it a second time? That is what it sounds like. If you bought them singly and you paid separate postage for each, then I think the seller is more or less obliged to send them separately, to cover himself with tracking?
In any case, it sounds as if you are only getting one more flashdrive than you originally wanted so it isn't the end of the world, you can gift it or keep it for later.
I am not sure how the payment for the flashdrives went through with the book purchase without you seeing the total price at any stage.
I think you can contact ebay via chat, as others have suggested, but I am not sure you will get anywhere. You bid on the flashdrives separately by the sounds of it, you bought, you paid.
If you find you have a problem with any purchase that arrives, it is faulty or not as described (or if an item does not arrive) then you can open an ebay claim for a refund. I think it would be worth reading up about that as in your feedback you say you have been scammed in the past. You should only open a claim though if an item is significantly not as described.
