Three ways to make sure a toxic person you not longer want around won't contact you again.
a. Call him/her about 5 times each day....pester that person with your calls...
b. Be always very late / absent...
c. Say / do those things you know upset them...
You may say "Well, I always can tell him /her I don't want to continue the friendship."
The problem with certain individuals is they need to be the ones ending the friendship...otherwise they may become stalkers and dangerous.