What can I do to stop collection agency from skip tracing?

My mortgage company has repeatedly contacted the parents of my boyfriend in hopes of reaching me. I've asked them to stop calling them. They said they would and noted my account. I am in the negotiation process of modifying my home loan- I am current but usually late so they'll immediately start calling me. I will answer the phone once to at least talk to them and give them the heads up that I am paying my mortgage and to stop calling me five times day—I just pay late. It’s beginning to become a nuisance for his parents who are frustrated they’re receiving calls. If I don’t immediately answer the phone (usually because I am at work during the day), they skip trace to those who “may know me” the same day. How do I get them to stop? Send them a certified letter to cease and desist? I could understand if I just ignore the mortgage company but I don’t!! I understand the industry is in turmoil right now but not everyone is in the same catagory of losing their homes!!