PIP delays to send a review form to assessor

My son has had a review back in June of this year. He has had no acknowledgement of the receipt of his form (although we know they received it as we posted it back special delivery) I rang them last week to find out what was happening and I was told ‘it is in a queue waiting to go to the assessor’ ?? There is no accountability at all and the operative could give me no more details on how long this queue is and when it is likely that he will hear. What will happen if his PIP is downgraded? Will he have to pay back any money due to their delays? (I am not expecting it to be downgraded but you never know with all these cut backs!)