I would start by calling PayPal, as it is easier to ignore an email complaint than it is to ignore phone calls. Set aside a morning for it as they can be a little obstructive initially - but if you have the facts to hand (why they restricted you, why this reason no longer applies, when the restriction began, etc.) and set out your complaint clearly, they may left the restriction as they will feel it's less effort to do so than to keep arguing with you.