Negative reviews used by competitors to tarnish your reputation is nothing new. I faced the same troubles with my website. The best you can do is to notify Google and you already did, rest leave it up to them.
You can notify the team at Google regarding a violation of their review policy by flagging the specific review.
When flagging a review:
A) If you can, have several people flag the review in question. There is power in numbers and it’s possible it may help increase awareness and ideally action.
B) Once a review is flagged try to wait a couple of days for a response or ideally for it to be removed, however; if the review is loaded with hate-speech, profanity, and/or has highly sensitive content, I would say escalate it immediately. Flag and report, then immediately contact a Google support team member.
Yes flagged them with huge numbers if possible for you. Reply them and ask their identity, If they are not your genuine customer they will not have any answer. It will show up to everyone that you and your company is decent and analyze that comment is absolutely fake