MBD worst company!

I have rent-master attending to a tenant of mine MBD does not show their number on call when phoning it comes up as unknown, plus they are harassing me who has nothing to do with the account and has to receive money from rent master and threatening me with legal stuff. I have send emails phoned requested call backs and to no avail every time I ask for them to correct the account or liaise with rent master to get the correct info and stop phoning me some calls very late at night and some calls as early as 6 am . Does these people buy their degrees. When can I get the right help and why am I being harassed when it is a tenant that should be contacted. Plus why threaten me with blacklisting.