what do i do if a auction company sells my item without my final approval

The company assured me that only in the event where I'm happy with an offer would my item be sold. They set the minimum price for my item ask me to choose the set minimum so the bidding could start. but then accept a final offer and sold the item without getting my consent. The bidding process or what to expect was never explained to me. All that was explained to me was that in the event i did not like an offer i did not have to accept it. By setting the minimum bid I expected them to come and run a final offer through me before making any final step which I was very much entitled to. I allowed to list my item I never gave them ownership over it nor did I sign any paper that confirms such transfer of ownership. Less than two hours after receiving an email telling me that my item was sold at a price that i was not happy with. I immediately emailed the company asking them to stop all transactions until all misgivings were resolved.