You can ask the DWP for a mandatory reconsideration, normally within one month of the date on your decision letter, explaining why you disagree and providing any supporting evidence. If the decision stays the same, you can appeal to an independent tribunal, usually by submitting the required form online or by post. PIP is generally not paid while a new claim is refused, although arrangements can differ if an existing award is being challenged. Check the official GOV.UK guidance and consider getting help from a welfare rights adviser or Citizens Advice.