If you have anything indicating your prior enrollment in the course, you may want to bring it with you when you attempt to gain re-entry into the course. Evidence of prior enrollment does not guarantee re-enrollment into the course and such evidence in no way obligates anyone to allow you back into the course. Contact the department to find out how they are handling the course. The general rule is that it is at the instructor's discretion to allow a student into a closed course. However, this can vary depending on the department and course.
Some departments keep waiting lists while others insist that enrollment be purely via touchtone.
That is to say, if you can't touchtone into the course then you can't get into the course.