Call your local police department and file a report. However, if your daughter is still using, she may get caught up in the results also, The probation officer won't discuss his case with you back will probably listen to you so go ahead and call, I would try and make sure you can be discreet as you don't want your daughter in any danger.
A call to to the minor's probation officer is certainly one approach to take, and hopefully that JPO will do something about the situtation.
Another possibility is to obtain an injunction against harassment against this individual who continues to contact your daughter over your objections. If your daughter is under 18, you can file the request for the injunction on her behalf.
You must be careful about what you tell the judge to whom you present the petition for injunction about your daughter's use of drugs. However, that is not the purpose of the petition. The purpose is to keep this bad influence away from your daughter. Once you have obtained the injunction, he may challenge it, but that would probably not be a good idea for him if you have saved the text messages he has sent regarding providing your daughter with drugs.
Once the injunction is in place, if he contacts your daughter again, you may call the police and he can be arrested for violating a court order. He can still be proceeded against by his probation officer.