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.