Bazgrim's post in Sold by mistake my goth´s clothes. Now can´t buy it back was marked as the answer
Do you remember which vendor you sold it to?
If so, go back to that vendor, open up the buyback tab.
On the PC version the "Buy" button to buy back Goth stuff does not work, however, if you double click it (press the button your controller twice) with the Goth piece selected in the buyback window it will allow you to purchase it back from the vendor you sold it to.