If you have already written a letter of complaint, and it is in process, then I suggest that you print out copies of that letter, with another covering letter, referring the recipient to the consultant dealing with your complaint.
Then every time someone contacts you by phone, ask them for their name, job title, email or postal address, and tell them that you are sending them a complaint letter.
If they harrass you in a group, or singly at appointments, just pull the letters out of your bag and hand them out, asking for the name and job title of each person.
Be sure to mention 'scaremongering' 'harrassment' 'bullying' and 'emotional blackmail' in your covering letter.
Obviously, you don't go around threatening people with these. You act perfectly polite and compliant until they start in on you with the pressure, and then you respond, politely, by handing them the letter and explaining that this subject is not open for discussion. Then refuse to engage further until the subject is changed.