Hi Dave,
many of us do receive such and the best way of dealing it to simply report them.
fiverr don't allow outside communication or any handling to make a fair platform for everyone to help and share.
It also protect you and your work to work on the fiverr rather to communicate outside.
I suggest you to block or report those users and if matter continuous just drop a ticket on fiverr support to resolve the matter.
I hope this will help.