I am excuse of letting a mental disable client during something that I didn't say at all how can this be resol?

If you should have doubts about another person,if they lie on you about a situtation that is not true,that is false allegations,and you are about to lose your job.A client at a group home lied on me and said that I told him to start the van up this morning,than I get a call from the director who me out completing.