PIP renewals

Is it common practice for PIP not to have medical reviews for renewals and extend an award for a year rather than just renewing same? My son is autistic and is really stressed as renewal due in June and after 8 months after the renewal application went in he hasn't heard anything. We keep ringing but he cannot cope when we wait 40 minutes plus to someone who doesn't seem to know much. Also what happens to his mobility car meanwhile which he has had for the last five years and they will not extend the contract again