So the question was asked, "what can be done if community service was not completed and it was my final chance? Will I be sentenced to jail?"
When a defendant is given multiple chances to perform community service and fails to do so, jail is certainly a possibility. Judges feel that you were given a considerable break in sentencing and that you are not taking it seriously or giving it the priority it deserves. Your first step once community service is missed, is to go back to the office where you signed up, ASAP, explain the reasons for missing your community service and ask politely to reschedule your missed date(s). Unfortunately many counties are very inflexible in allowing missed dates to be rescheduled. Perhaps it is so that they are not inundated with requests to reschedule which would lead to defendants essentially doing the community service when they felt like it rather than when they were ordered to. Make sure you document the date and time of who you spoke to as well as their name.
Assuming the community service office was unable or unwilling to reschedule your missed dates, reach out to your attorney and ask them to intervene on your behalf. They too should document their efforts. If neither of these solutions work, I recommend that you do the community service anyway. Take the initiative to find a non-profit organization, speak to someone in charge and ask them how you go about volunteering. Complete all of the missed hours with this company BEFORE your court date. Ask a supervisor in the non-profit company to write a letter to the judge on the company stationery, explaining what the charity does, the dates and times you volunteered, and what tasks you performed during those hours. They should provide their contact information in case a court clerk needs to verify this information.
Now this strategy is not guaranteed to keep the judge from re-sentencing you to jail but it should maximize that possibility as you did complete the hours just not in the manner proposed. The judge will likely allow you to reschedule your missed time with the program originally intended.