Harrassing a NON-client

These people phoned me 5 times this morning, wanting to know when their client (my sister) would make payment. I told them I am not even in the same province as her, but will pass on the message. When they kept phoning me, I told them to please take me off their system or at least make a note that they've already phoned today.... How dare I?! I was then told that only the account holder (my sister) can instruct them to remove my number from their system... even though it's my number and I never authorized her or Donna to use my number. The cheek. Simply blocked the rude nr from my phone. Can't imagine how they treat their actual clients....