Can an employer falsely accuse you? please read!!!!?

ok, yesterday i got fired for speaking my mind and today i have my boss show up on my doorstep claiming that my mother called them and left a threatening message saying of you think my daughter is phsyco then you haven't met her phsyco mother yet. this was left on my bosses cell phone which my mom doesn't have the number to, when i called and asked to hear the msg they told me it was deleted and they didn't think it was my mom after all, i asked for the number which the voice mail was left from they told me they couldn't give it to me, what are my rights here do i have any? can the accuse me of this and not give me any information about it?!