Better known as the Elephant Repellant Fallacy — a claim that a preventative is working when, in fact, the thing it prevents rarely or never happens anyway.
"Hey you better buy my elephant repellant so you don't get attacked!"
'Okay.'
...
"So were you attacked?"
'No, I live in San Francisco and there are no wild elephants."
"Hey you better buy my elephant repellant so you don't get attacked!"
'Okay.'
...
"So were you attacked?"
'No, I live in San Francisco and there are no wild elephants."
"Well, I guess the repellant is working!"