Basically it's supposed to be a double form of perennial - Japanese bindweed. I googled and there are some references to the plant possibly being sterile, or seed not growing true. If yours was a result of root division then you SHOULD have a clone of the parent plant. Clearly it's more like a bindweed. I would send your photos to the supplier with a request for a replacement or a refund.

waitaki - I'm surprised that a business in France would send rhizomes to the US because technically it would require you to have an import permit or the plant (including rhizomes) to be shipped with a phytosanitary certificate as per USDA regulations.

The double flowered sterile form of Calystegia known as "Flore Pleno" is actually Calystegia pubescens , but often mislabeled otherwise...

What I see in the photo of the plant that somehow grew is Calystegia sepium , which is commonly spread by birds or seed eating rodents...

There is certainly the possibility that the suppliers stock has been contaminated with the wrong species or that whatever they sent you died and the more adapted Calystegia sepium volunteered in your growing area.....

Perhaps the company may be willing to replace it , but if their stock is contaminated , then you might just get the same plant that you got the 1st time...