Your public defender should be able to explain the status of your probation on the prior charge. Or you can check with the court (or look at the court file associated with the charge).

A probation violation is based on probable cause, not proof beyond a reasonable doubt, so you can be convicted of a probation violation even if you are acquitted of criminal charges from the same incident. Also, depending upon the terms of your probation, you may be subject to violation proceedings just for getting arrested. Missing a court date would also typically be grounds for violation, although that would normally be excused if it truly resulted from court error.

If you are not happy with your public defender, consider retaining a private criminal defense lawyer.