If your status has not yet changed, you should be able to use PTO in the interim as per the rules for your still-current status. The problem you face is that if your employer will not let you use the PTO, to force them to let you do so, you'd have to sue your employer, which has obvious costs, in terms of time, in terms of money, and in terms of the relationship with the employer; however, there is no way other than legal action to force them to let you use your PTO. You have to decide if legal action is worth it to you.