AAwww Keith, are you seeing someone else!
Anyway, that sound fishy to me! And 100? is quiet a mistake as well. Would be curious what is the amount on the bill in the box.
If it says 344?, well, that's it. You paid what is on the bill, end of story.
You can send it back also, he must pay for it (European law if you return it within 7 days), but you will need to ask the money upfront, as he might refund it without the shipping cost, and you end up at loss!
Tricky one I have to say. I would get the package, check the bill, and take it from here.
On a side note, I have to say, and unfortunately, I very very rarely order anything from the UK. Last time I did, they tried to get me on shipping (International shipping... For Ireland, when an European shipping was available... Excuse was Ireland was an Island... No sh#t Sherlock! So I had to pay triple. I get anything shipped from Germany, Italy, France at a fraction of the cost from anywhere in the UK).