I spoke to a customer service representative and he put me in to the voice mail of one of the owners. I left a message saying something to the effect of "I would appreciate you not spamming us, I know it's likely an outside company but could you ask them to stop".
I fully did not expect to hear from the owner but to his credit, he just called me to apologize and let me know that he would take care of the situation. He said, "since you contacted me old-school, I decided to do the same". He was a stand up guy about it and said he'd do his best to have the company he employs not use Hubski anymore.
I take him at his word, he was a nice guy.