Report it through your Business Profile (find the review → flag → pick the violation), and expect honesty: Google only removes reviews that violate its policies — spam, conflicts of interest, off-topic, profanity. 'Unfair and untrue' alone often doesn't qualify, and removal decisions take days and frequently decline.
While it's pending, reply publicly and calmly for the audience that matters — future customers reading it: state you have no record of them as a customer, invite them to contact you directly. Composed beats combative, every time.
The durable defense is arithmetic: steady real reviews shrink any fake one to noise. One bad entry in 80 reads like an outlier; in 8, it reads like a warning.