I'm not sure if this is the proper way to handle it, but my N-ex-boyfriend used to gas light me all the time. I would record everything and keep screen shots of his texts and chat convos to prove myself but even then it wasn't good enough.

I would say "My experiences are real and how I perceive things is perfectly valid and acceptable." I would often walk away and go about doing my business then it would eventually drop.

This seems to work on my Nmother but she'll start yelling and screaming. At that point I say: "No amount of yelling or screaming at me will make my experience less valid." or "I accept your perspective on things, but my experience and perspective is valid because I am allowed to see things my way too." and again not speak further on it.

I often remind myself once alone that I am not to blame for their behavior, and state to myself that my experiences are valid.