The Essentials of Universal Credit

Grandson aged 22 just finished residential college, been told  by LA he should claim UC and if does not LA will assume he has it and charge for care services to be provided. He is entitled to full PIP including mobility, though as yet this has not been reinstated since his return from college, despite numerous phone calls.
Not sure where to start to support him (he is fully dependant physically and mentally). Parent on benefits but not been granted carers allowance for over a year for vacations and unable to find exact details why, told been overpaid in past but no details of how much or why. Letters of complaint ignored.
Any advice appreciated. thanks