When a player is blacklisted, there are a number of things they can do to continue their harassment, including standing on top of a player, emoting on or at them, trading them, and other disruptive behaviors without needing to type.
You can actually report this as this is against TOS. SE will take actions even if they are following you around and you tell them to leave them alone. They are very strict with their harrassement policy.

My suggestion is to make it so that if you blacklist a player, they become invisible client-side so that only you cannot see them. Make it so the offending player is effectively de-rendered. This alone would halt many of their attempts of harassment after they are blacklisted. Make it so they are only visible during duties where you need to work together.
They are. If you block a person you cannot see them ingame anymore and you will not queued up with them in duties.