You have to plead guilty in order to be given DEJ.
Unfortunately for you, this means that if you violate, you will immediately be sentenced;
if you complete the drug program, pay the probation costs & court fines & do not vioolate any laws, then, in 18 months, the court can term/dismiss your case.
After the court granted DEJ, you should have been ordered to report to Probation (usu within 48 or 72 hours of sentencing). The court will advise which probation office (not always the closest).
...are you sure you were granted DEJ ?
Were you sent to Probation ?
What did your atty tell you ? Call the PD and ask what happened (I assume you had the Public Defender). ...Did they send you to Probaton for a pre-qualification for DEJ?
Don't sit and wait for someone to contact you - get off your butt and find out what happened to you in court. Once you plead, you have to take care not to violate any of the terms of probation. 'I didn't know' isn't going to work for you.