no payments

What would you advise someone to do.if they wasn't paid pip daily living for 4 years because of a technical issue. And you didn't know you were entitled to it until you had a review and applied for a upgrade from just mobility component.and they said you already have pip living. And you have to beg them to look at payments and see no payments have been paid.but for 4 years you were missing out on all the other benifits and a dons you could have claimed and received. It mind bogged to not know how much that someone missed out on.