Blake and Associates harassment calls

I have a huge problem with these debt collectors, I asked them nicely to stop calling me on my office line as it blocks all incoming calls businesses wise, and that disturbs my work. Their excuse is that I “always block their calls” of which I don’t. How can one block a call when they use different numbers? These people are harassing me, they don’t take instructions from me and should this continue to happen I will take the matter further. This is against the law and I will sue them should this harassment continue.