Old Mutual Finance keeps calling my work

Old mutual finance keeps calling my work and asking for the HR number. Our reception and various other people has already told them NOT to call at work as we may NOT receive personal calls. Instead they keep calling and calling. Putting the phone down and then immediately calling again requesting to speak to me. How many times must our reception/switboard tell them we are not allowed personal calls? I have send them an arrangement for the accounts via email and still they keep trying to call my work. THis will be the last time i instruct them not to call me at work. Next i will report them to the Debt Collection Society for not adhering to the laws of debt collecting.