Unauthorized upgrades to a business account

Vodacom call center calls numbers on my Business account and doing unauthorized upgrades to lines. First of all this is Harassment as I did not give them consent to contact any of the associated numbers and secondly its ***** as anytime I want something done on any of my numbers I have to provide a letterhead giving permission in writing! I sincerely hope this can be sorted out if not I will be moving to MTN!