Court system messed up and now want to retry case after guilty plea accepted

My son & fiancé were pulled over for speeding. As a result they were also charged with possession. They hired an attorney, went to court believing (because their attorney asked them about all the charges) that their appearance was for everything related to the matter. My sons fiancé took responsibility for the possession charge, plead guilty and is on probation. 2 days later we got a letter in mail saying my sons license was being suspended for failure to appear. We called only to find out the speeding ticket wasn't included in the case he just appeared for. After some back and forth they set a court date for the speeding ticket. Found out today that the new court date is for the entire case to be tried over again. How is that possible? They can not afford to pay attorneys fees etc all over again. My son wants to fight the ticket because he already has to many points against his license & the vehicle they were driving had speedometer issues. Please advise.