Do I have to pay a 4 year old juvenile ticket if I was incarcerated at the time of the court date?

I got a few tickets (pot,not paaying for bus) when I was 14. I am now 20 ,but at the time of the court dates was incarcerated for vioaling probation. I was told this could be time served? any helpful ways to go about this wouls be appreciated because now Im getting a bill for $690.00 before I can get my licencse.