Nearly every time I have a bad experience with a company the problem is systemic, but a bad rating will be associated with the random person who served me. So I don't participate. If the problem is particularly bad I find another supplier.
If they did their job, I'll give them the "you did your job" 5 stars.
Even if the company has systemic problems, they still need to pay bills as long as they still have the job.
Finding another company is a smart option. I'd also write to the management to explain why that problem is blocking you from doing business with them, without mentioning who you spoke with.
Nearly every time I have a bad experience with a company the problem is systemic, but a bad rating will be associated with the random person who served me. So I don't participate. If the problem is particularly bad I find another supplier.