Dupe with Syndicate Medallion

I wanted to sell a syndicate medallion to faust but the items didnt dissapear was still in my inventory.Now when i saw that i cancel the trade and receive another medallion.I tried this two more time and the same result.Now i have 4 medallions.
Fix this bug this is dupping.I just want my medallion fuck the other 3.

Sounds more like you bought Medallions instead of selling them (gets reported quite a lot). Without any video, screenshot, or bug report number, there is no way to prove either way.