Call blocker might be of some help. Also don't pick up on numbers you do not recognize, or where there are caller IDs that seem odd. Or where there is no caller ID
I got through by blocking my number (*67) then dialing their number and they answered something Diabetic. I asked for my number to be removed I gave it and she says one moment and then hung up on me. So we'll see if she actually did remove my number.
Repeatedly call x2 day, up to five calls a day. Leave no message. This is not a reputable service. Should be reported to Michigan Attorney General or Michigan State Police. Let them explain it to someone in authority.