If a seller harasses you for a low rating, you can report them for review manipulation by forwarding their emails to community-help@amazon.com, including the product link and relevant information. For other methods of contact, take pictures/screenshots and send them to the same email.
You can also respond to the seller using this template:
You have violated Amazon’s Terms of Service by using my private contact information to ask me to change my review.
I will not change my review for your product as that is unethical and unfair to other customers. Please use the feedback in my review to improve the product for future customers.
I have reported you to Amazon for asking me to change my review. Please do not contact me again.
If the seller is offering compensation (gift cards, free product, etc) for writing or editing your reviews, you can report them at https://account-status.amazon.com/report-review-compensation