hello,im from WA and have a traffic question my son is 19…

hello,im from WA and have a traffic question
my son is 19 on his green Ps he was nabbed by the hoon laws a few wks ago because his car was too noisy when accelarating! I his father, found this a bit harsh! the police came to our house took the car away and it was impounded for 28 days,and yellow stickerd, my son since has got his car back,the car has had new exhaust fitted and sticker removed.
3 wks later notice came through post to say he will loose his licence for three months,not having had anything like this happen before,i thought have i got any legal standing to try and keep my sons licence and his job. He does not cause any problems on the roads he has a good job which he needs his licence, as we all do! he was aparently spotted accelarating heavily by an off duty police officer,i would suggest mybe some wheel spin, but there is or was no black mark on road afterwards.
he was leaving a well known tyre shop who he deals with through his work, yes probably showing off a little to mates!
I called a lawyer too see if was any chance we could keep his licence,she said with good references there was good chance in court, and he was to plead guilty,My son got lots of exellent references from his work, the tyre shop was first reluctent as the manager there said he should not plead guilty as he thought a rediculous charge as there is many cars louder than my sons was, but they sent a great reference to him anyway. we went to court with our solicitor she said she expected a $600 fine maybe some conditions, we came out the judge told him off and warnd him she would not be so kind to him if she saw him in there again,she saw from the references he was well repected by all, she said he would keep his licence and was find $300+ court charges.
we were very happy with this outcome, as my boy can keep his job for which he now needs to help pay off about $2500 that his car has cost since this all started, with storage charges, exahaust etc!
yesterday we are informed by post, his licence is cancelled! which it has been backdated from court date! he has been driving company vehicles for last 2 wks!
our solicitor says it seems the licencing department has now charged him with section 51 I ask what is that?? it seems to me there is the police department then there is licencing department with its own laws?
can we be helped do you think?? All my life i have belived a judges word to be final?
Thankyou