How can you disprove it if you have no evidence to back you up?
OK, so you can lie through your teeth and insist that you phoned me and we had a conversation, coz I can't prove you didn't. It gets worse, if -God forbid- you should die and your family insist you phoned me and had a conversation with me, I'm in an even more difficult situation because you haven't got the opportunity of telling the truth.