toasti is correct, here you can find an (excellent) list of the most difficult sport climbing, bouldering and free solo problems (9b+/15C but also 15B/9b etc.). The spreadsheet lists sources for each first ascent (FA). It contains not only FAs but also repeats (and differentiate between proposed and repeaters' grades). Grades are French / Font:
The source confirms toasti's answer. La Dura Dura in Oliana, Spain, is yet the only 9b+ which has been confirmed by the repeater. There are however two other 9b+ (Change at Flatanger, Norway, and Vasil Vasil at Sloup, Czech Republic) and one 9c (Silence at Flatanger) firstly ascended by Adam Ondra which have not been repeated (and for that reason have not been confirmed).
Update: Since I received a down vote, I want to clarify that I am not the creator of the spreadsheet nor do I know him. Yet, I think this source is an interesting link for everyone who is interested in the question asked (or similar questions).