Before you decide to buy this to change your name, you should check if it’s available! Unfortunately, there is no easy way to check for the availability of a name. Only after you’ve purchased the name change is when you’re able to enter your desired username. But, a workaround is to create a new character, skip past all the creation and then input your username on the last screen to see if the desired name you want is available.
By the way…
If you are looking for a way to avoid a certain player who seems to be constantly harassing you, these other solutions might help assist you better. You can use the “/ignore PlayerName” command to prevent a player from being able to communicate with you. But, if someone is seriously griefing and disrupting your gameplay, then you should probably look towards sending support a ticket with evidence of the harassment. (screenshot/video footage)