Sure sounds to me like Toyota should replace that tire under the Road Hazard warranty. If I were you I would replace that tire immediately, at your own expense as seems necessary, then file a claim for reimbursement directly with Toyota (see the Road Hazard brochure that came with your Prius for the procedure to follow). If you saved all your paperwork from the various repair attempts, as well as the sales receipt from your new tire purchase, this should be a no-brainer. Good luck! And let us know how this turns out.