Just because you received rent from Section 8 doesn't mean the tenant is still there. It just means that they have not reported a change of residence/status to Section 8.
I don't know what your state or lease allows, but if it were me (under Ky laws/my lease) I would serve a 48-hour notice of entry (those pesky smoke detectors, furnace filters, etc) as well as either an Urgent Late or PQ notice. Remember, Section 8 should receive a copy of any notice you give the tenant. You would be amazed at what a tenant will do if they feel their Section 8 benefits could be jeopardized by not adhering to the lease or responding to the local office.
Whatever you decide to do, don't procrastinate any longer - the longer you wait the more it will cost you.