My apt complex said they are going to charge me if I dont list them as an "interested party" on my renters...?

I have lived in the same Apt Complex for 5 years. I have had renters insurance the entire time (I wouldn't be without it). The apartment manager left a note on my door that said unless I added them as an "interested party" immediately, they would start charging me $25 per month until I do. I have already provided them proof that I have insurance and my agent that their request is not legal.It is also no where in the lease that they will charge if I don't list them. It doesn't even state that they will charge if I don't have insurance.