Long time Amazon Seller here.
It's against Amazon TOS to contact Amazon's customers outside the Amazon messaging system, and they are really heavy handed against sellers breaching this.
If you complain to Amazon that the seller is contacting you outside the Amazon messaging platform and harrassing you, then Amazon will close their seller account.
Alternatively you can threaten to report them to Amazon for this and they will go away.
I had a seller hassle me on my personal email after me telling them to stop asking for removal of an honest review in exchange for a replacement of a poorly made product.
Literally could not find a way to tell Amazon, so I left a review on their seller page.
Amazon deleted that review because "product was fulfilled by Amazon"
If you complain to Amazon that the seller is contacting you outside the Amazon messaging platform and harrassing you, then Amazon will close their seller account.
Alternatively you can threaten to report them to Amazon for this and they will go away.