Jeweller selling one's jewellery without permission

I went to a jeweller with some items of old gold jewellery to to get new jewellery. He gave me 2 options:

1. He melts the old jewellery and makes new ones and I pay him for his labour.

2. If there is some piece of jewellery which I like, we can swop the both.

I told him give me some time to decide. In the meantime, he sent me a picture of an item which was also gold which I liked, so I told him to please keep it for me and I will come to his office and we'll make the deal.

When I finally go there, he informs me that in order to keep that item for me, he had to swop my jewellery for it. This was done without first asking me and without my permission. So now my jewellery is gone and he tells me I must take the new item. I asked him regarding the difference in weights of the two as both were gold. His reply was "the difference was very small, don't worry about it".

My problem is that I understand that him doing that straight swop was not permissible according to shariah as gold for gold must be exact and even a "small difference" is not permissible. But now my jewellery is gone and cannot be retrieved, and I'm left with no option but to take this new item. What do I do in this situation? Will I be sinful for taking this item knowing that he got it through a riba transaction? And if I don't take it, I will lose out as he wouldn't pay me for my gold.

Also, with regard to the difference in the weights, I don't even know which was more or less as he wouldn't tell me clearly (although it seems to me that mine was the more).